http://www.renntech.org/forums/index.php?showtopic=15&st=0&#entry24
There have been 4 generations of the seal. When I had the part number checked it was about 2 years ago and I think it was for generation 3. The parts guy told me how many of those seals had been sold by my dealer. I did not ask but I doubt he could tell me how many were sold in the world - but Porsche can.
If you put a part number in the computer you can search the history. It will tell you former and present part numbers. I did not ask the parts guy to do this.
If someone has a cooperative parts guy ask if he can tell how many of each style seal has been sold at the dealership.