Sunroof Diagnosis

[salguod]

I'm starting to dig into my non-functional sunroof. Well, more like poorly functional, I guess.

The previous owner stopped using the sunroof when a year or two ago he heard a scrape when closing it and found a long scratch on the driver's side paint on the sunroof panel. It was closed, so he left it that way.

I haven't touched it until today. It opens to the vent position fine, and the inner panel retracts. It then closes, but the inner panel does not close from the vent position. Is this normal?

When I try to retract it, nearly immediately the rear part of the sunroof drops with a bang, like it's not connected to something. When closing there's a scraping sound from the driver's side and the scratch in the paint. Is the drop-with-a-bang normal? Any idea what that might indicate?

I think my next step is to drop the headliner (it needs replaced anyway) and see what I can see. I'd rather not have to pull the entire cassette to diagnose it, but it seems that I might have to.

Any ideas on what might be wrong?