Be sure you understand how the thing works - go in the back, find the micro switches and motor assembly, and make sure that everything is tightened. There is a little screw - I mean tiny- that seems to want to work itself off the unit. Check this area closely and if you can't find the screw, just look around the back and drag one of those magnet tools around so that you might pick it up.
I recommend that you have a few extra plastic gears because when you might chew up a few while getting
the thing adjusted properly. It's a real PITA.
When I did this job on my '87 944 about 4 years ago, I remember thinking that I would pay someone to do this job the next time. <img src="/forum/images/smilies/968/wink.gif" class="smilie" alt="" /> I found a great DIY on this site:
www.clarks-garage.com
Hope it helps.
-Scott