The sunroof in my "wife's car", the '87 TD has the same problem. With the roof popped up I could see that a bracket on the driver's side had broken. It is the driver's side that won't budge. I read somewhere that the whole headliner has to come down and the sunroof taken aprt to gain access. On top of that the part it'self is about $85. Well, I guess that's what A/C is for. This makes me appreciate the manual sunroof in my '83 TD.

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1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member