Pass door locks by itself

[BillM]

My cousin has a 86 Westy with manual locks. The one
on her pass side is having issues. The lock knob falls
down over bumps. It has no resistance when you push
down on it. It still locks and unlocks but any bump or
even when you just close the door,the knob falls down
into the locked position.
I need to go fix it this weekend and wondering what I may
need for parts. I have never had any issues with the locks
on any of my vans so havent really messed with them.
Any experienced advice would be appreciated so I can take
care of this in one trip. Thanks.
_________________
Bill M
87 Westy