Was washing my car the other day and I noticed some stains on my bumper that looked like oil or something. It has that look as if its in the paint but I'm positive it wasn't there before. I tried everything (on an inconspicuous area) and it didn't work. I even used a rubbing compound with no results. Does the fact that the bumper is plastic make stains "stick" more? Any suggestions on what else I can try?