Black streaks (Under Window)

There is a product made just for that and it's been around for decades, "Starbrite Black Streak Remover", it's available at most large auto parts stores and on Amazon, or just Google it and find the nearest store that carries it. I use it on both painted aluminum and fiberglass, doesn't harm it. Just spray it on and wash it off with a soapy sponge, really easy. Also, put a good paste wax, not polish, on those areas and the streaks will take much longer to appear and when you first notice them they'll wipe off with a dry soft cloth such as an old T shirt.

Nick