There is a product called On and Off...you wear gloves and ppaint it on with a brush but it really works to get stains off gelcoat finishes. It is normally used to remove the brown water line stains that boats get when sitting in the water at moorage but it also removes rust and other stains that cleaners won't even touch. Try it on a small area and see. It is available at West Marine and Boater's World I know.