my "new" 126 300sd had only one working power window when I got it, and 2 of the repairs were nothing more than replacing a bolt or screw.

the drivers side has missing teeth on the end of the large geared ring.
the window would run up to about 1" from top and stop and grind there.

my fix: weld new material onto the piece and grind new teeth into it. worked smashingly well. teeth aren't perfect, but they seem to work.
try it yourself. use a piece of masking tape to line up where the new teeth ought to be cut.
I'll try to remember to post before and after pics.

Karl