If some type of switch could be installed, so when the window nears the top it would stop the motor.
I saw this switch on a 190E today in PNP and searched the # 002 545 01 14, and it comes up as a W0133-1623395 here in Fast lane.
maybe something like this could work?
My 85 300D had one of these on the VC that did something?
Charlie