The rear window seam separating from the top is getting to be a somewhat common problem on Z3s.
It happened on my car after about 4.5 years.
Repairing this turns out to be pretty easy. I used 'Permatex Black Silicon
Adhesive Sealant' which can be purchased at most auto parts stores. Also
used a small amount of rubbing alcohol, 3M Painters tape, a small screwdriver,
a shop rag or two and an drum brake adjustment tool.
First off I masked of the area of the sepearation. This would help to keep
me from making a mess of the rest of the top.
I used a little bit of rubbing alcohol on the shop rag to clean the area behind the seperation so the glue could get a good bond. Make sure after you clean the area you give enough time for the alcohol to fully evaporate.
After that I used the applicator tip on the Permatex cut off very near the top so I would get a small bead of glue. Then just filled in a good amount of the area behind the pull and squeezed the top parts together and wiped away and glue that squished out. I used the brake adjusting tool simply to help push the fabric together with the other hand reaching in the window and holding the back side of the top. I also tucked the edge down slightly.
I held them together for about 20-25 minutes then just left the car alone in the garage so the glue had time to cure. I gave it about 22 hours before I drove or touched it.
Update: Still holding together after almost 2 years.