w201 sunroof stopped working
 

At least it was in the fully closed position. My sunroof is supposed to drop down and slide back. Motor is making a clicking noise, like broken gears, when I try to open it (switch is not marked, so may be when I try to close it) You can hear the motor do something in both directions, the one clicks like broken gears, the other just sounds like the motor loading up.

Any thoughts on the cause of failure? too dark right now to bother, will check it out in the morning. Some help with common failure points would help.

you probably have a broken cord at the attachment to the sliding roof.

the clicking is you trying to close the roof and the clutch slipping.

wind the motor up (running noise) then pry the roof open and remove the interior cover.

you will find a broken harness at the rear center of the roof

if you can't get it open, the cord may have stripped worm gears at the motor.

w201 sunroof stopped working
 

The same grinding was happening on my recently acquired 1894 190d. Problem was a stripped nylon gear. I found a replacement gear at PicknPull for about five bucks. To install it, I...
1) Removed the left trunk (boot) liner.
2) Removed the two screws holding the antenna to the body.
3) Loosened the collar at the bottom of the antenna mast.
4) Pulled off the cover of the sunroof manual operating nut.
5) Removed the nut under the cover.
6) Removed the three bolts holding the sunroof motor in place.
7) Rotated the sunroof motor to remove the gear cover at the back.
8) Pulled out the plastic gear.
9) Lubed the new gear with plastic gear grease (got grease on line)
10) Re-assembled everything up to the point of replacing the cover of the manual operating nut. This nut adjusts the clutch tension.
11) Using trial and error, gave it enough clutch tension to operate the roof without stripping the gears.
12) After reading lots of discussion re-rail lube, I went the cheap route and used "SiliKroil" spray on a rag.