I just had some wide clear packing tape handy and used a strip of that trimmed with scissors to fit the contour of the shape. The crack was close to the edge.
Since I never put the top down the tape help up pretty good. The tape was not that noticeable even to me via the rear view mirror and I forget how long the repair lasted. I may have replaced the tape once when it finally fell prey to the elements.
If the window is bad enough for tape -- and especially if you want to continue to put the top down -- you should get the window replaced.
There are two ways of doing this -- so I've been told. I've only had it done one way. The way it was done for my car was the old window was cut out leaving a narrow outline of its plastic still in the top canvas -- the portion fo the window that is stitched to the top. The new window was sewn in using a separate line of stitches. This created a bit of a raised border aroudn the window -- under the canvas -- but was not really noticeable. My biggest concern was was the new window water tight.
It was.
And the new window held up real well though I still didn't put the top down any.
The other way -- a top shop in Santa Clara told me it uses this technique -- is to remove all remnants of the old top and then sew in the new top. I don't recall if the new top gets sewn in using the same stiching pattern as the old top or if the new top gets a new lne of stitching.
If you elect to get a new window you'll have to ask around about this and pick the replacement technique you feel is best.
The new window lasted as long as the top did, approx. another 7 years. Then the top developed a leak about in the center of the top just ahead of the rear window. In rain or when washing some drops of water would run down the inside of the back window.
Because of the risk to the car's electronics: the secureity module on teh cabin floor under the passenger seat and the engine's control unit afixed to the front bulkhead of the rear trunk I had the top replaced. The guy at the top shop said the old top didn't look that bad but of course a leak is a leak.
While I preferred to keep the car "factory" a new Porsche top even with a discount was around $3K not including installation. I elected to go with the GAHH top and so far it has proved to be the equal to the factory top though I do not lower the top so I don't know how the GAHH top would hold up with more top movement.