I'd use something a little stronger than mineral spirits, say acetone or naptha, but only with good ventilation and nitrile gloves. If a simple wash won't do it, you may be looking at a need for serious solvent action, which you may or may not be comfortable doing at home. If so, lacquer thinner will clean just about anything off anything, but it's nasty stuff. Again, don't forget the gloves and ventilation.