Had to replace door latch and actuator assembly recently on my daughter's 91 164B driver's door for same reason. Key would lock door but not unlock door. Key and lock were OK but something in latch going bad.
With window up you can remove rear window track and then remove complete latch and actuator assembly. I just replaced whole thing and may try to figure out what is wrong with old one as it now seems to work once I got it out.
Maybe you can play with yours and get it working again if nothing broken.
With window up you can remove rear window track and then remove complete latch and actuator assembly. I just replaced whole thing and may try to figure out what is wrong with old one as it now seems to work once I got it out.
Maybe you can play with yours and get it working again if nothing broken.