Most boat owners with older boats have dealt with mildew at one time or another. It'll penetrate into vinyl and stain it and also on single stage paint (with no clear coat). Rubbing compound may work if it's just on top of the surface, but if it's deep into the paint that you'll be removing a lot of paint to remove the mold/mildew. The only product that I have found that is highly affective is called Marine 31. Just spray it on and let it sit for a few minutes and then watch mildew disappear. Try to get the "non-gel" version if you can find it which is a lot more affective. I've never had a bad reaction with it before but it's a good idea to try it on a test spot first.