i'm almost positive that the wiper was contacting the full curve of the rear window when i bought the car but now it's not making contact at the top, therefore not making a perfect arcing sweep.
RE: e320 wagon rear wiper not making contact at top
I was having a similar problem with the front wiper blade on my '98. I bought an aftermarket wiper blade assembly. Mistake. Worse. I replaced it with the MB unit and it works fine.
I also replaced the rear wiper and it works well. Full coverage. I hope that helps and good luck.
RE: e320 wagon rear wiper not making contact at top
I replaced my blade, made very little difference. The car was in for service, they replaced the blade under warranty, also very little difference. Its so minor I wont get bent out of shape, nothing to see in that area anyway!