The part is a little round plastic cover (~1.5 inches in diameter) that covers the round hole that the cabriolet hard top release bolts sit down in. These holes are next to the covers for the spring loaded roll-over bars behind the back seats.
The part number is 996.555.457.00
The soft top caught the seatback cover and apparently made one of these little covers fly off (gone!) It's just a little ABS plastic piece but I can't find a replacement anywhere !
Thanks in advance.

 

If you call any Porsche dealership parts dept. and give them that part number they will look it up and know what it is and they will be able to order that peice for you.

 

If you have any trouble, let me know....

I AM the Plug Guy, you know.

 

Thanks 03C4S, Ric found that little part for me. Really nice guy.