[Excaliber]

I had a similiar problem and used some polishing compound to attack it. I got some of the spots off but it left the area I was working on a little "dull". Polishing compound does have some very very small abrasive qualities that act like a "cleaning" agent. Rubbing compound is more aggressive on the same idea of polishing. Of course there are MANY different grades of rubbing compound, like there is sand paper.

I took my car to a professional detailer to finish removing the white marks I had. He wouldn't reveal what he did, but it looked way better than what I did!