you can open them up fairly easily.
I did to repair my drivers one.
It is fairly self explanatory when you take the unit out, there are just some clips that you can ease open.
There is a small spring in the other end of the arm. this gives you the ratchet. either thats popped out or the other end has snapped which seems to be the common failure.
Probably worth 5 mins to strip it and take a look