1989 300SE Driver's side wiper problem.
 

Hello,
My drivers side wiper arm moves past the window then hangs up. It was working fine but now it appears that something is either wrong in the linkage or that there is some sort of adjustment to tighten the arm to the motor. The passenger side works fine. And I can move the driver's side where it begins to work again, then works for 1 or 2 wipes, then it goes beyond the wipe range and locks into the windshield channel. Does anyone have any thoughts on this? Is there a linkage mecnahism? Are there two motors? Is there a way to tighten the arm to the motor? Any input will be greatly apprecaited. Thank you.

I'm guessing that the serrations on the pivot post and/or the arm have worn to the point where the arm isn't securely attached anymore, despite the nut being tight (which I assume you have already checked, and assuming also your wiper arm attachment is the same as on my 380SE).
I have been able to fix such a situation by applying a coat of JB Weld to the pivot post, a smear of grease on the hole on the arm (so the arm doesn't get bonded to the post), then re-attach. The JB Weld will find its way into the worn serrations and provide enough friction when set-up to hold the arm when the nut is tightened.
You're probably looking at a new arm and maybe a new post/linkage piece for a proper repair.....