Don't bother with this. Accept that the sun roof will not function. Mine did the same thing. It turned out that the problem is with sun roof cassette. This is the large black rim mechanism which mounts to the sheet metal. It typically needs to be replaced. In order to do that you must remove the headliner and glass. The part is very expensive. BMW quoted around $2000 just for the part. Labor was going to be another $2000. The sunroof, while I love it was not worth $4000 to me. I got the back shut as you did and I just don't touch it anymore