I just got done washing my car, and I always have a lot of black on the bumper from my exhaust but it all usually comes off. Today it didn't I have two huge spots that no matter how hard I scrubbed wouldn't come off. I might try simple green to get it off, it's all I have around here. Has anyone else had this problem? Me and the guy who sold me the car get along very well and he emails to make sure everything is okay with the car every so often, should I call him and say something?