Try Krud Kutter. You can get it in the paint department at Home Depot. It is a paint remover/cleaner and be careful with it as it may work too well. As with any non-petroleum based cleaner, rinse the surface well with water and let it dry at least overnight. Paint in warm weather (does the sun shine in Socal?). Another thing to try is Goof Off. I used this a couple of times on metal surfaces, but not on fiberglass or plastic.