painting my 71 dart bumpers...

You can try some of 0000 steel wool (think thats that finest). It cleaned most of the aging on my and left a respectable shine. No scratching that I can tell, it won't remove any pitting. I hit mine with a coat of wax after the polishing. I know that guy flying in the 737 over my house at 35000 feets thinks they are niiiiice!!