LOOK OUT VPM!
You may want to make sure that the roof is sliding freely. The sunroof rails , I have read, are at least part of the problem if the motor eats the gear.
In other words, replacing the motor/gear may not solve the problem and the gear will get eaten up again
I'd be real interested to hear how you do.
'84 190E 2.3
'83 Porsche 944 (track car)
'84 Porsche 944 (parts car)
85.5 Porsche 944 (sled)