93 SC2 automatic seat belts binding

My girlfriend's seat belts don't work properly. They appear to move forward far enough, but do not move far enough back when they should. They only move about 5" back. You can hear a motor or something running and it eventually stops.

They BOTH do this. So it's likely the box which controls them, right?

I found a TSB which might be about this (92-T-11B) but don't have a copy of it.

And, will the tracks and motor from an SL-series fit this thing? I haven't been able to verify if they are the same part.

Thanks for any help.