A long shot, but the brace that supports the door lock solenoid is prone to breakage. You would need to pull the door trim panel and look at the bracket that the solenoid attaches to to determine if it is cracked or broken as miaalignment will cause the problem you describe (hapened on my 1988 750 and I had a friend weld the backet together and that was not easy as the metal is very fragile). Go to bmwe32.masscom.net for a good look at how to resolve the issue. This is Johan and Seans site and it is invaluable for E32 owners.