Hi folks,
I found a way to make my window tight:
After dissambly of the door panels (one hook broke, because Haynes Repair manual is useless for LS1 models, although stated otherwise) I found two fixing screws and one adjustment screw for the triangular mounting bracket of the side mirror. You can bend the bracket inwards to press harder against the rubber seal of the windshield frame.
The window is still closing smoothly.
Wind noise is reduced considerably and no more leaking in the car wash. I have shown this to my Garage mechanic. They admitted that they have only english written manuals and do not understand them
You can find a picture here
http://www.geocities.com/gunnar_lindner/GLCP1
Cheers!
Gunnar