89 535i Door Lock Problem

When I try to lock/unlock the doors on my 89 535i, the passenger door lock doesn't go down all the way or won't come up all the way, leaving my door either locked or unlocked. This also happens with other doors from time to time but mostly with just the passenger. Every now and then it will work fine for a couple days but then go back to this... making it very annoying. Does anyone have a fix?

I had a similar problem, maybe this will help. I found that if I left my trunk lock in a position other than nuetral, it caused my door locks to act up. When you access your trunk just make sure you return the key slot to the vertical.