I am not sure what you are describing. But it sounds to me that the oil soaked into the unpainted area because the surface is not protected with wax and maybe a little chalky. It wiped of the painted area because the paint did not allow the oil to penetrate into the gel coat underneath. If this is the case if a solvent like acetone does not remove the stain completely you may have to use a polishing type compound. After removing the stain I would give the entire MH a good cleaning(removing the oxidation) then a good waxing to seal the surface. Oil should not penetrate a properly waxed FG surface.