HI. I've got an 84 240D and today my drivers side door made a loud sound and now it doesn't stay open (i'm not sure what the part is called, if someone could enlighten me). It's the mechanism that makes the door stop at two places when you open it.

went round to check the other doors and one rear door is definitely not as smooth as the rest and sounds like it's about ot break, it no longer rolls into the next position.

how can i fix the rear door? i've tried wd40 and didn't do much. are these things the same for every door?? and do i need to take the door off to get to them?