On my 89 780 the vent funtion never worked, i just assumed it was not a feature on the moonroof equip cars. Its not to hard to realign the sunroof to stop leaks.

You will need a Torx T6 i belive, not 100% on the size, remove the moonroof headliner and look into the tracks, there will be 1 Torx srew in front and one in rear, if you loosen them it will allow you to life and lower the moonroof, when you get it where you think it should be retighten and close, it might take a few tries but youll get it sealed up.

as for the stopping, it could be realted to the front arms that lift and low the metal bar, mine has never worked properly either and since i dont use it enough to be a bother i never botherd to repair/invetigate futher.