I've gone through replacing all window motors on the W124 and regulators don't go bad. I see no reason for it. I've heard that the "black" bolt is the adjustment for the regulator. Maybe pull off the panel and make sure all the nuts+bolts are tight and the window is sitting correctly on the guide rails.

I'll take some pics for you tomorrow although based on what you said in the previous post, I think we probably have different problems.

__________________
2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k