I don't know what a W201 or W124 wiper system looks like but it doesn't sound the same based on this thread W140 95S420 wiper question
, and my problem is not that it won't wipe but that the blade doesn't extend.
I've attached a photo of the linkage I see when I remove the plastic cover. The pivot point of this driver side arm is at the lower end of the short arm in the lower left of the photo. I can't see how to detach the aluminium case that contains this assembly from the drive shaft to what sort of cam is underneath. The wiper arm is free to move through its stroke in any wiper position of the wiper's swing so it seems to me that whatever type of cam dictates the blade's position is worn or off track.