MB recommends replacing the wiper blade every six months. With one intermitent delay setting, if you do not turn the wiper on and off and let it run dry, the blade life is shortened.
Cleaning the wiper blade with paper should prove beneficial. You will see a black film on the paper.
I have noticed that at times I cannot flow the traffic flow due to inadequate cleaning action of the mono wiper. I believe the newer MB's have dual wipers.
94 E320 58000 Miles