when you say you got an insert from the dealer, do you mean just the rubber refill that slides into the arm and contacts the window, or the entire arm, with the hinged metal piece as well? I would say that if you haven't bought the whole piece with metal and all, buy it and it will solve your problem (about $20 at parts shop). It did for me. I have an old 300e, but judging from the fastlane pic, our wipers look exactly the same. I think over time the arm just gets out of shape and does not arc over the curve of the windshield like it should.

__________________
headrivenoise... listen.