Many Porsche owners have found that the rear window wiper doesn't work well (or doesn't work at all). If you'd like to remove the old wiper motor & arm, this plug can provide a smooth, finished look. It has a satin black finish, measures about the size of a quarter, is made of solid steel. It comes with seals and attaching hardware for a quick installation.  

This specialty bolt is almost a perfect substitute for Porsche's $52 wiper delete plug. I say almost because you can see a small number stamped in the plug face. If you're really detail oriented, you may want to fill that with body filler or a thick coat of spray paint. Even as is, it is a very nice piece and offered at a very good a price.

This link will take you to some help on removing your old wiper arm/motor and installing "The Plug."