It looks like this problem is fairly common with the 190's. I did a search for "190 Sunroof" and there are plenty of threads, and one in particular with photos.

Hari, do you know if this particular sunroof is a "tilt and slide", or is it supposed to just slide back without tilt?

In either case, it looks like the key is removing the headliner section of the sunroof, which is held on with some kind of clips (shown somewhat in the photos). After getting the headliner out, it seems that the most common problems are broken or bent "gold clip", and or broken or bent tilt brackets, which are located on each side. I think there is a crossbar which engages both of the tilt brackets (if it's a tilt sunroof).

If you can figure out how to remove the headliner section without damaging it, I believe the rest is just nuts and bolts. I have personally always preferred nuts and bolts to any kind of upholstery, door panel, or headliner type of work. That being said, the MB's seem to be more forgiving of door panel and upholstery work than any US made autos I've worked on.

Steve.

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'93 190E/D 2.5 Turbodiesel 5-speed (daily driver)
'87 190D 2.5 Turbo rustbucket - parts car
'84 Dodge Rampage diesel - Land Speed Record Holder
'13 Ram 2500 Diesel
'05 Toyota 4Runner