the top corners of my window are always getting a black residue after a week or so. and the molding that it seals up on is starting to get worn so it's just rubbing off on the glass. anyone have the same issue? not a big deal yet but i've had it less than 10 months (bought new) and it's my first car with no extra metal running along the top of the window. is this just a common "wear and tear" thing?