[roadracer311]

Here's a great writeup about this subject:
http://www.renntech.org/forums/index.php?showtopic=14754&pid=73915&mode=threaded&start=#entry73915

I was just looking into this last night. The above link has the Porsche part numbers. I'm planning to order a pair of o-rings along with whatever I end up ordering next from sunset Porsche in Oregon.
http://www.sunsetporsche.com/porsche.php