Getting off black streaks

I've had good luck with WashWax All and keeping the roof clean. I have to say though since I have owned units with full body paint and frameless windows, and gutters, I see fewer black streaks.  I think the old gaskets are the root of a lot of the streaks. I think they degrade over time and the rain washes the residue down. If you notice, most black streaks are below some wall protrusion, like a window, outlet, bin door, awning arm, etc. That's because that's where the black gaskets are. I think paint and a good wax keeps the streaks from sticking/staining and the newer gaskets are less prone to breaking down.