Re: Results of my IMS replacement

Well, i got my car back today, along with the old IMS.

AutoHaus in Chatham NJ installed the LN kit.

Drumroll please.....

It was perfect. See pics. no sign whatsoever of wear.

Here's the data that might be reevant, or at least interesting:
2004 2.7M 37k miles ~20 track days ~25-30 autoX days Oil changed 1/yr or ~7k miles Always driven easy until oil is warm, then often driven with spirit, but it is a daily driver and i do have my license, so not TOO much spirit.



Another view:



When i spin the bearing there is no play at all. It actually does nto spin very freely - there is quite a bit of resistance, but its very, very smooth. I presume this results from the thick grease, and maybe the rubber seals.

Anyway, i thought some might like to know.

Anyway, i still feel better about it. The LN unit looks so well made, and its, well, new.

Grant

"Bart, with $10,000, we'd be millionaires! We could buy all kinds of useful things like...love!"

Grant, thanks for keeping us posted and the final results and pic. IMS issues have been hashed to bits here, but your post made me think of something we may never know - Does an IMS go bad in bits and pieces over a long period, or does it deteriote and implode very quickly? If the former, then maybe yours might have been good for 100k, but if the later, who knows, it might have blown next month. There has been speculation that the rubber goes bad and the grease is replaced my engine oil (or something like that). But, we will never know if this happens slowly or pretty much all at once. Bottom line, your origional IMS may look good now, but who knows what might have happened. I think it is was a good choice and gives more of piece of mind.

I appreciate your report. Though it looks to me like you wasted your money. Bearings fail slowly over time and your old one wasn't worn. The LN part has no guarantee and no track record. The manufacturer recommends you regularly pull of the transmission so it would be great to see your LN bearing after a year or so to see how much more wear it has than the Porsche part.

... since if it was clear that my money was well spent my motor would be scattered across Alton VA.

As it turned out, I clearly had no need of a replacement. But among my friends with boxsters, i have two failures. What's that, 2/maybe 30? ( I don't count this entire community since i don't know the actuals). That's 7%. Ouch.

OTOH the LN part is very well designed and made. Better materials, larger ( more surface area a sure-fire way to longer bearing life) and designed to catch splash lubrication, not to keep it out. Don't know if you've looked into it. I agonized. Even called timken! (not to mention HRH Pedro)

So i hope that i now have a permanent part. I have no intention of checking it every 30k miles. Clutch was out, time to do it.

Gene at Autohaus shares the concern that the LN part has no track record. The way i see it, however, the Porsche OEM part does, and its not a good one.

So if i spend, say $900 to get a better IMS bearing. And saved a $10-15k motor - money well spent. Or, as you note, not.

Grant

I understand your motivation for changing it. It basically comes down to peace of mind. In your case it was an expensive discovery that there was no looming issue.

My primary objection is that the LN part is a much higher risk than the OEM part. As the bearing engineer that posts here has stated, engine oil is not suitable for lubricating a bearing. And as I (and others) have stated, even if engine oil was suitable, splash lubrication is not enough to keep a fast-spinning bearing lubricated. This is what you get when you have a non-engineer trying to solve a complicated engineering issue. The LN bearings are probably less reliable than the OEM ones. "Using better/stronger materials" is not a solution because it doesn't address the root cause. And even if all of these things were not true, the bearing has not been fully tested. That fact alone makes it higher risk.

Boxsterra,

Please reread my posts. Engine oil is a suitable bearing lubricant IF the viscosity and/or speed is sufficient to prevent metal to metal contact. 0-40 has too low a viscosity. 15-50 is better.
Water will work if the loads are light and the speeds are high enough but I don't recommend it. ( many high speed bearings are lubed with an air/oil mist) Oil splash will remove debris and cool the bearing contact surfaces. Grease won't. Seals are meant to keep dirt out, not lube in.
The LN retrofit is a definite improvement. Larger bearings or more of them reduce the point loads allowing a less viscous oil to work.

I hope Charles will send me one of his bearings when/if he has a failed one.

Ed B
The bearing engineer

the bearing is subject to much more contamination?

If its me, define open bearing. Do you mean the LN IMS is not sealed and is exposed to all that motor oil? Well, ... yea. OK. But oil's pretty clean stuff overall. We expose our crankshafts, timing gear, camshafts, hydraulic lifters, etc etc to that oil and none of them seem to have failure problems. In fact, there motors seem to go 200k if the IMS can keep its balls in its races. I guess i'm saying our "dirty" oil is better than clean, but nonexistengt, grease.

The point is not if a sealed, clean, full, bearing with the ideal factory grease is better than an identically made bearing that relies on engine oil. Its whether a bearing that is smaller, softer, and has grease seals that are known to deteriorate with heat, and then essentially goes dry, is superior to one that is designed to operate in the imperfect environment. And as i have now said 4 times, the answer may be "no" - but all evidence i have seen suggests "probably". Did Jake call you names or something? :-)

Powertech had a table full of Dead IMSs. Some came from dead engines, two from cars that were right there being worked on that miraculously still ran. They were toast. No seals. Scarred races. Missing balls (lots missing!) truly amazing stuff.

Grant

Not necessarily. An IMS bearing without seals receives clean filtered oil in a closed environment provided you change the oil and filter as recommended. An open bearing on a piece of construction equipment wont last regardless of what the lube is.
A sealed, greased bearing will not last as long as an open bearing continuously lubed with clean oil.
Grease is a mixture of oil and a thickener. Common thickeners are sodium or lithium soaps, silicone or micro refined clay. They are not lubricants. Additives include molybdenum disulfide, teflon and others. These are solids. Seals wear and the particles find there way into a bearing. Solid lubricants are only effective on sliding surfaces.
Oils can be natural organic or synthetic. The extreme contact pressure between a ball and ball groove, (very small area, as high as 350000 psi), cauuses heat that oxidizes oil creating solid particles. With a greased bearing there is very little oil and most have no way of relubing.

This ends the bearing lesson for the week.

Ed B



Edited 1 time(s). Last edit at 01/29/2011 09:48AM by Ed B. (view changes)

So, if i read between the lines and apply to the LN bearing, the splash lubrication may in fact be *better*....right?

Grant

Right. I'll take oil splash lubrication over grease any time. It's a little hard to splash lube wheel bearings, though.

Ed B

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Boxsterra
My primary objection is that the LN part is a much higher risk than the OEM part. As the bearing engineer that posts here has stated, engine oil is not suitable for lubricating a bearing. And as I (and others) have stated, even if engine oil was suitable, splash lubrication is not enough to keep a fast-spinning bearing lubricated.

This may be a stupid question, but doesn't the crankshaft in any engine have bearings that support it, and aren't those bearings lubricated by engine oil? If engine oil doesn't lubricate the crankshaft bearings, what does?

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paulwdenton

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Boxsterra
My primary objection is that the LN part is a much higher risk than the OEM part. As the bearing engineer that posts here has stated, engine oil is not suitable for lubricating a bearing. And as I (and others) have stated, even if engine oil was suitable, splash lubrication is not enough to keep a fast-spinning bearing lubricated.

This may be a stupid question, but doesn't the crankshaft in any engine have bearings that support it, and aren't those bearings lubricated by engine oil? If engine oil doesn't lubricate the crankshaft bearings, what does?

and even rods. The 4-cam 356 engine is an example in a car.

Many motorcycle engines have ball/roller bearing cranks. Most (all) of my motorcycle engines including my '74 H-D Sportster. Check that all. My '71 Honda CB0-750 had a plain bearing crank IIRC.

In our Boxster engines though (and all modern car engines) the crank main and rod bearings are plain bearings -- no moving parts -- and rely upon an oil film. The 'bearing' in this case is the oil film. It is only a fraction of a thousandth of an inch thick, but the very tight clearance coupled with a bunch of other factors can have these plain bearings last forever.

Anyhow, engine oil most certainly does lubricate the main/rod and camshaft bearings (these are plain too) and cool them as well. (The oil of course lubes every moving part in the engine. The rings/pistons/cylinder interface is a bearing, a sliding bearing.)

Sincerely,

MarcW.

I wont even begin to address that one. Suffice it to say my motor oil formulation engineer friends will take you up on that debate! If you want, please say more, but do so in gory detail. At the moment i'm not buying the pure assertion. Unless its as simple as "super thin oil creates a thin and weak barrier". True enough, btu not revelatory.

But harder and stronger materials does begin to solve the problem. It may be brute force, but if the bearing is to be subjected to less than optimal lubrication, then you want it to be durable. The force per unit area is inversely proportional to the area, as is heat, and as is the danger of going from hydrodynamic lubrication to barrier.

I agree that thicker oils are better for this, and for that and many other reasons i have been a broken record that the 0w40 Porsche recommends is not an optimal choice. I typically mix it with 15w50 or replace it with Syntec 10w40 or rotella-T 5w40.

Thickness of oil as a f(x) of weight, of course, depends on temperature as well. So saying that 0w40 or 5w30 is insufficient begs the question "when and where?". In alaska? Perfectly fine.

I continue to ack that your main point "we don't have data on the LN unit" is valid. Only time will tell.

I will also re-iterate that we DO have history on Porsche's solution, and it was not pleasant. However, if we do E(value) analysis and a sufficiently low failure probability, its money spent poorly. Then again, so is most insurance.

I wonder why the new motors have no IMS. Hmmm? Porsche knows something...?

Grant

Lets assume just for a second that the rate of failure for whatever causes of the original IMS part has been ~.5% per motor year (I choose that figure, though I think it too high, because it approximates 1k failures per year based on the 200k plus Boxsters running around. I really think the figure is less than half that.) Since ~1,800 of the LN part have been installed, we should have heard of some failures in the LN part if they failed at the same rate since some have been installed 24 months (test items 30 months). We haven't heard of a single failure. Does that mean a true zero percent probability/possibility of failure? Or just such a small number it hasn't shown up yet? Or a statistical freak? I don't know. They don't either.

How much testing will convince you? I ask that because I really got on Jake in a public forum (I think the old PPB over this very issue. How can you be sure? How can you duplicate the testing Porsche does and even they were wrong? Where are your 20 test mules some running 100k miles? His reply was a candid, we can't. Only time will tell. Which is something Charles says too. They did believe in the theory enough to put it in their personal cars and a wife's car that she runs the heck out of. That was 30 months ago.

My last email conversation with Charles was he was going to see if he couldn't arrange with some of the early adapters with the most mileage to have their LN bearings pulled/swapped just so Ed could analyze them. And they could all get a better sense of their projected longevity.

..of course, it just might turn out to be the best advertising he could do. Despite the fact that i put one in, it was not an easy decision to go with an unproven part, and many 9obviously) are more skeptical than me, or you.

Grant

Edited 1 time(s). Last edit at 01/30/2011 04:27AM by Stephen Tinker in Australia...... (view changes)

I'm coming from a different angle, where in Australia a 10 year old 986 S is worth $40,000 and is still worth keeping - as apposed to the "do I part it out" syndrome prevalent in the US and UK....

As a purely selfish financial exercise, I replaced my IMS bearing (together with the clutch and RMS) at 46,000 miles last September. I installed the LN bearing assembly and when I removed one side of the old bearing seal, no old oil was evident and the bearing was still quite stiff when trying to spin it. Grease was evident internally and no oil leaked out when the bearing placed on tissue paper.
I may be a lucky one, or perhaps 99% of us are lucky. Maybe its because my oil has been replaced every 5-6000 miles since new, who knows. What I do know is that inspecting the LN upgraded parts compared to the originals, there isn't a comparison. If the LN bearing assembly breaks, I'm in no worse a position (comparatively speaking) than if the Porsche part fails....



Edited 1 time(s). Last edit at 01/30/2011 04:28AM by Stephen Tinker in Australia...... (view changes)

We have "the sky is falling" group versus the "I don't see the sky falling here with my head in the sand" group.

The thing is, this car is a blast but wold be much more enjoyable if I wasn't aware of the IMS issue. Sometimes wish I'd never ventured onto the great world wide web for information. Now that I know what I think I know, I don't know what I'll do!

"I'm certainly uncertain, at least I'm pretty sure I am"
(Missed the Boat - Modest Mouse)

dghii
2000 Boxster S 6speed 112k miles

Quote
dghii
We have "the sky is falling" group versus the "I don't see the sky falling here with my head in the sand" group.

... there's also the: "I won't let the sky fall on my head" 'cause I'm gonna fix it before it fails, group.
I'm kinda one of those.

Happy Boxstering,
Pedro

Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

---

Racecar spelled backwards is Racecar

"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"

"If you wait, all that happens is that you get older"... Mario Andretti

"Being second is to be the first of the ones who lose" ... Ayrton Senna

And i am now in that space. Rightly or wrongly.

Grant

Neither.

I'm in the "The sky is falling for some people. There's a very low probability it's you so just drive and enjoy." group.

The failure rate of the OEM bearing in the first 3 years/30k miles is probably far less than 1 in 10,000. And pretty much all of the existing LN bearings are in that category. So I would be surprised if any had failed.

I can appreciate their admission that the longevity of the bearing cannot be determined experimentally in the lab without better equipment than they have. This is exactly why critical car parts aren't made by small shops. And it is also exactly why car manufacturers put their critical parts through rigorous testing.

Ceramic is a great material for bearings but I seriously question about how long it will last with only splash lubrication.



Edited 1 time(s). Last edit at 01/28/2011 11:06PM by Boxsterra. (view changes)

But also see my longer answer wherever the board placed it.....its the old story - i need not outrun the bear, only you :-)

Only the guy that wrote the check can decide if the money was wasted. If he feels more comfortable or better about the car because of the changes, he may well conclude that this is money well spent. One less thing to worry about?

Having said that, the lack of wear on this part is impressive. I second the question on seeing about getting the seals off to look at the grease.

Total 911 magazine recently had an article on IMS failures and they feel it is rare and exaggerated on message boards. Unfortunately only those who have problems squeal about it on message boards. What we have is sampling error. No one in the Porsche club in Alabama has had this problem that I am aware of. The local indys say they dint see it.

Extended warranty.....money much better spent

Interesting the people in the Alabama dont see ims problems and the local indys dont ever see it . Two companys offer an upgraded bearing , motor rebuild companys sell reman motors on ebay and my buddy who sells used parts gets a call a week from people looking for replacement 2.7 and 3.2 motors. We are also seeing 996 and 986 cars on salvage yard web sites that have suffered engine fires???? I bet if the adjusters took a bore scope and checked they would find the motor died before the fire. Page 60 of Dempseys book covers the replacement of IMS bearings , I replaced my motor , one member replaced two motors , I have taken apart a failed 2.5 motor and the local indy has seen one blown 3.2 and replaced two bad bearing . L&N have classes which they fill on repairing theses motors and still we hear its not a problem!!! Grant you did not waste your money

Not to flame anyone on here, but no one -- and I repeat, no one -- knows the extent of IMS failures but Porsche. There are many, many incidences of IMS failures reported. My opinion, based only on my gut from what I've read, is that this is a serious manufacturing defect that can't be ignored and, if you look at the depressed values for used Boxsters, the market seems to be behind me on that. However, as some have pointed out, the attention to those incidents may be causing us to exaggerate the real situation. On the other hand, we have Porsche fanatics who downplay the situation, perhaps because they have drunk the Kool-Aid, fear that their own cars will be tainted and resale values will go down even further. I don't know who's right, but any estimate of IMS failures on here should be taken as nothing more than guesses unless the poster can verify that PCNA has authorized him/her to release the actual numbers.

Now, some questions for the OP (grant): I may have missed it, but could you go over the parts/labor costs again for the LN repair? Did you simply find a local mechanic who would agree to do the fix and then order the necessary parts from Raby? I'm interested to know because I may want to have this repair done myself. Thanks.

Navarro does.

Raby found the hand holding was too expensive in time for the profit on the sale. He prefers to be responsible for the ones he does rather than try to support all those who try but then have problems some of which may have nothing to do with the part he sold.

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longislander1

Now, some questions for the OP (grant): I may have missed it, but could you go over the parts/labor costs again for the LN repair? Did you simply find a local mechanic who would agree to do the fix and then order the necessary parts from Raby? I'm interested to know because I may want to have this repair done myself. Thanks.

Sorry i missed this. I bought the part from LN engineering (Charles). About $600 plus tools (removal tool, install tool, cam lock tool(s)). I then paid my local porsche specialist [autohaus in Chatham, NJ, part of the PCA tech team BTW] to do the rms and the IMS when the clutch was already out, saving a great deal of general labor. note that while its not that hard to do, the documentation of little details is very, very sparse. So someone who's done this before may be preferred. Once the tranny is out, its only a few hours max, btu its sensitive work, locking timing chains, pressing the bearing off the shaft, etc.

Grant

Thanks. Might be worth it for me down the line if I can find a mechanic here on Long Island. Although at around 14K miles (with extreme hibernation this winter), the Boxster may not need a clutch replacement for some time. Plus, I've been thinking of giving it up for something older and more collectible -- an asset that isn't declining in value, but still offers some fun.

Quote
TSS4LSU
Total 911 magazine recently had an article on IMS failures and they feel it is rare and exaggerated on message boards. Unfortunately only those who have problems squeal about it on message boards. What we have is sampling error. No one in the Porsche club in Alabama has had this problem that I am aware of. The local indys say they dint see it.

Extended warranty.....money much better spent

I looked at the article and here's what they had to say after interviewing the two independent "experts":

"So, should early 996s be avoided? Nick and Steve each admit that they wouldn’t themselves buy one, but are keen to point out that the problems they’ve discussed probably affect five to ten percent of early 996 engines. In other words, there are plenty out there that are running fine. Of course, though, no one knows what will happen in the future."

Not exactly a ringing endorsement. Plus, another couple of guys guessing without any facts to back it up.

a failures per car/year figure. 5 to 10% failures on a car that can be 13 years old is far different than the same % on a 1 or 2 year old car. Not that we know if any of these percentage estimates (including ones I've used in discussions) are even close to accurate. Most of the samples are too small. Which is why I track and publish the number of installs and the length of the longest on Charles's part. So you'll know the best figures and can draw your own conclusions. Most of those were installed as the result of forum chatter and so I figure if there are any failures we'll hear about them the same way.

Of course how many failures of the originals will occur while we are waiting for proof? We won't know that either. And I note a big drop off in problem reports of originals recently. Most of our cars must be in storage. Look for a spike when they get taken out for the first time?

Maybe on reason mine was in good condition is that it is driven and equipped with 4 snow tires. Donuts and drifting in the snow is far too fun to miss.

Grant

Do you drive your car year round or store it? could you remove the rubber seal and see if you have oil or grease inside? thanks

I drive my car year round. In fact i has snow tires on it at the moment. Its a commuter-plaything-grocery_getter-racecar (sorry i spelled that backwards on ya)

I'd be happy to open it up for the forum, unless Charles wants it back. Something about a warranty. I need to send him an email, unless h's lurking here :-)

Grant

grant set the bearing up right on a piece of clean cardboard if my theory is correct we should see a an oil stain begin to form after a time. I'm am wondering if southern cars driven all year have this problem less often than a stored car . If the bearing grease is being replaced by engine oil then to me it makes sense that the oil will slowly run out over the 5 months of inactivity, since the oil is not supposed to be in the bearing ,the replacement of that oil may take some time by then the bearing is already on its way out. I was talking to a indy yesterday who repairs Volkswagen's and he is seeing a sealed bearing in one of there motors that will seize causing a lot of damage. Maybe if your talking to Charles at L&N ask him if he is seeing more northern (stored) cars with bad bearings.

You plan to keep your car so you decided to pursue a path that gave you piece of mind.

Some folks fear their car as their warranty runs out and trade it in on a brand new model claiming the decision to be financially wise by avoiding a potentially costly repair that may or may not ever appear.

Which is money better spent?

Enjoy you car!

dghii
2000 Boxster S 6speed 112k miles

even if i wind up with another along the way. From what i see, these motors - in fact the whole cars - last a long,long time. Except that some unknown % go boom in a big way when the valves and the pistons get in a fistfight (funny, so do Audis, when the TB breaks - another religious argument among the faithful - for the record, i replace TB and water pumps regularly too - and they cost more than IMSs)

So yes, i feel very good about it. The part is huge. The bearings are grown ceramic jobbies from timken. The races make the original look like a toy. And, most importantly, the back is designed to catch splashing oil and channel it into the race.

This has another benefit. It gives you a solid reason to rev that puppy so it will splash. Sorry officer, i'm just lubricating my bearings. Hmmmm.

He might think you have some strange pleasure.

Grant

I sure would like to see the inside of the old bearing with the grease seal removed. Seems like the seal would eventually let a little oil inside and wash out the grease but I'm no expert. If there's still grease in your old unit it would prove me wrong.

All the sealed IMS bearings I have examined have no obvious grease in them. Just a little dirty oil.

Ed B

... and sharing your info.

To me, the issue with the IMS bearing in the M96 engine is that we have to look at it as a wear item.

Because of the stress at the end of the crankshaft, or because the block is in two pieces, or because the bearing is sealed, or just because...
... we should keep an eye (and ear and nose) on it.

Whenever the tranny needs to be removed for whatever, I'd check it.
Whenever you see any metal in your oil filter, I'd check it.
Whenever you discern a new noise in the area, I'd check it.
Whenever you see an oil seepage with rancid smell under the bellhousing I'd check it.

But having said that, I still think that it's a small percentage of the engines that grenade because of the IMS bearing.
I'm starting to believe that a lot of the damaged ones had RMS leaks which eventually damaged the elastometer in the dual mass flywheel.
This causes extra (unbalanced) rotation which in turn transfers to all of the engine's bearings.

I installed the LNE retrofit (dual row) bearing in my car after the OEM bearing lasted 196,000 miles.
I'm hoping that the new, ceramic bearing will last as long as the original, but I guess we'll just have to wait.

I really never worried too much about it and I'm not worrying about it now.

My next engine improvement will be the installation of an Accusump system (which I'll document).
If you track your car regularly, especially with track tires, I believe it's a MUST.

Happy Boxstering,
Pedro

Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

---

Racecar spelled backwards is Racecar

"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"

"If you wait, all that happens is that you get older"... Mario Andretti

"Being second is to be the first of the ones who lose" ... Ayrton Senna

Anytime you have the car hooked up to a PIWIS or Durametric system, check the CPS deviation values (or the actual cam values when the VarioCam is active); if the values are steady (particularly during RPM transitions from increasing to decreasing), the IMS is probably fine. But if (particularly at an idle) the deviation values are moving back and forth, pull the oil and filter looking for the ferrous granular material indicative of the IMS going south………..

“Anything really new is invented only in one’s youth. Later, one becomes more experienced, more famous – and more stupid.” - Albert Einstein

Pedro, from what I have been reading most of the problems so far have been to pre-2007 models. I surmise there is not enough time yet to determine if the problem persists. Assuming that it has not been "fixed", I also understand that it is not practical at this time to replace the IMS in the later models. Is that correct?
mike

... on both counts.
The '07s are still too new (as compared with the 986s).
Also, after MY '06 Porsche did a band-aid fix by beefing up the single row IMS; but by the same token the IMS can only be serviced by opening the engine.
The problem was "fixed" by Porsche when they came out with the new non IMS engine (9A1) 2.9 and 3.4 liter engines.
Happy Boxstering,
Pedro

Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

---

Racecar spelled backwards is Racecar

"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"

"If you wait, all that happens is that you get older"... Mario Andretti

"Being second is to be the first of the ones who lose" ... Ayrton Senna

At first blush, my OE IMS bearing seemed fine. It felt tight like you described yours. But then I tried a couple of things. Hold the outer race and try to move the inner race in a wobbling motion, as if the supported shaft were moving in a conical motion. Mine had some play. Next, pull the seals and see if there is any grease in the bearing. Mine had none; and there was engine oil inside the seals.

While I recognize it is anecdotal in nature, if the bearing is sealed to retain the grease and there is no grease in it, it is not operating in the manner in which it was intended to be used. While the oil inside the end of the IMS is not, as Pedro points out, fresh, clean, and in great supply, I'm comfortable that I'm better off with a bearing that is designed to be lubricated by oil that is actually lubricated by oil than with a bearing that is designed to be lubricated by a "lifetime" supply of grease that is actually being lubricated by a doubly limited (IMS cavity and the grease seal) supply of oil.

We most likely will never know the right answer, but the cost of checking/replacing this bearing when the clutch is replaced is a relatively low price for peace of mind. Since there is insufficient scientific evidence to draw a conclusion one way or another it becomes a personal preference. Each person must decide what makes them comfortable.

I probably would not have done this as a preventative measure by itself, but since I had the transmission out for a seal replacement (the IMS support plate O-ring was seeping) it seemed a good idea to replace the bearing along with the RMS as preventative medicine. My clutch was close to gone, so I replaced it as well.