"Newbie" Mike has resurrected my ancient sunroof problem. After not finding a response or answer to this, I took the problem to a mechanic friend of mine, who gave me a L shaped broken-off piece about 3/4 " on the shorter leg and 1.75" on the longer, that he said was blocking the track. I think it was actually part of the track. But it still didn't pop us, so I opened it and sprayed it with WD-30 and ran the sunroof back and forth about 12 times. Each time it got easier and easier to do. When it stopped getting easier and faster and less noisy, I pulled down on the thingie, and it popped up!
Of course, I still had the piece of what appears to be pot metal or some zinc-aluminum blend, and took it to Finish Line, who sell all sorts of German car parts here in Miami. They said that the factory had decided that the sunroof design on the 124 was deficient and had come out with a kit to correct the breaking track problem. The kit is said to cost around $60 to $80. At $72 per hour for installation that Gunter and Helmut will charge me for their always useful expertise, I am quite content to leave the money in a fund where it might earn $72 by the time I really need to fix it or get out the duct tape.
But since my sunroof now pops up and opens and closes and does not leak, I have decided to ignore the fact that a piece has broken off, since everything works and all I need to do is to spray all the pieces that appear to move with WD-30 every month or two.
As I recall, I needed to push gently upward on the right side or the sunroof in mid-pop for the first two or three times, and now it needs no help from me. I suppose that the lubricant needed time to ooze in.
So you can get the kit from the dealer, or try to fish out the broken part, and don't forget the WD-40.