A few weeks ago I went to the dealership to replace my wiper blades. The OEM blades are ridiculously overpriced, so I told them just to just replace the rubber inserts. Well, the other day in a rainstorm one of the blades was leaving behind a black residue. Is that at all normal for new rubber? And yesterday I noticed a few vertical hair-width scratches (although I can't actually feel them) on the drivers side of the windshield. Could the wiper blade have caused those scratches? Should I just replace the blades?