I have a PPW Z and I noticed while washing the car a couple days ago that the rear bumper looked pretty clean but then i would dry it after washing it and if my fingernail would rub against the rear bumper it would literally like scratch off some of the darker residue that i didnt even know was there (i assume from exhaust and it being a white car). So i rubbed away a portion of about 4" by 4" but once the car starts to dry it is then very hard to rub anymore of it off. So now im left with a 4x4 portion of my rear bumper that looks a little more white than the rest. Is it possible that a claybar would remove the rest of this stuff on my whole bumper? does anyone have a CLUE what im talkin about? I dont feel like using my fingernail to rub the entire rear bumper next time to get it all the same whiteness (haha)....