HZ,
A 993 targa pro over on rennlist ( Mike J) has been helping me out with the 993 targa top. These are some detailed pictures he has
https://plus.google.com/photos/106666807984086342852/albums/5742550549617206929?banner=pwa
Have a look and let me know. It appears the rear window does indeed have a rubber trim and not just window sealer. Do you have the aluminum trim riveted underneath the targa top that you can see in the pictures?