I have the power sunroof in my 83 240D. It's been closed and weather tight since I bought the car a few years ago. I will not tempt fate and try to open it. At least, not until every single other "issue" with the car has been addressed (which will probably be never).
IMHO, the sunroof was the most idiotic option ever designed for any car.
"Hey guys, I have a great idea, let's put giant hole in the roof (directly above the driver and passenger) and seal it with a sliding panel of metal or glass. What could possibly go wrong?" SMH