Job done
!
Ripped the windows out and renewed the rubber seal too.
Leaking came from the foam sealing strips between deck and frame, which were in poor condition and were replaced with butyl tape.
Replacing the rubber seal between aluminium frame and acrylic was pretty difficult due to the tight fit of the rubber seal, which made sliding together the 2 parts of the frame nearly impossible. First i tried lubricating it with liquid soap with no success and then with vaseline and pressing the halves together with 2 sturdy clamps i got both parts together to secure it with the 4 screws.
Another problem were the screws, which hold the aluminium frame down to the coach roof. It seems that bavaria had cut the hole for the window sightly too big, so some of the screwholes at the corners were only 1mm away from the border and the srews ran away and got no grip to tie the frame down to the roof. So i replaced the screws to machine screws with big washers and nuts on the inner side to apply sufficient pressure to the seal.