The earlier versions seemed to be worse then the later, but It has been my experience that they have a limited life and the warning signs are not totally transparent(partially due to location). If you have that many miles on it, then good for you. Personally, it is not worth risking the family getting stuck out here where service is not easy. In my view, the life of these coolant tanks depends on a number of varying factors:
-service life
-production date
-type of driving
-where it is driven(hot or cold climates)
You get the idea. Overall, I believe these cars run on the hot side and tend to cycle a lot. We've done a number of mods(3rd rad, 996 oil cooler, etc.) to counter this which I believe is helpful when sitting in stop and go traffic during the summer months. I've seen too many failures to for go the risk of an unexpected breakdown. Generally, I find on the VW/Audi marks(coolant tank is easily visable for cracking/leakage), 60k is a safe time for replacement before letting it go till the end of the service life when more damage could be risked. Even if the tank blows from air in the system, they should have the integrity to bleed that air from the system, and or the coolant system is being improperly serviced. It just shows the loss of structural integrity of the tank through the heat cycling. $208 for me, is cheap insurance towards reducing unexpected breakdowns. In my view, plastics have there limitations, especially as they age.
regards