I'm looking for a good product that can be applied to black exterior plastic. There are plenty of products that make the plastic look good when applied, but I've yet to find one that repels dirt well for a decent period of time. By that I mean, when I wash the car, I soak it with water first to soften any dirt, then I wash with water and car shampoo. The dirt comes off the car bodywork easily, but the black plastic has to be rubbed really hard, or scrubbed to remove marks. My car isn't very old, so it isn't just a matter of making the plastic look shiny again as it's already in good condition, I just want something that's easy to wash. Many thanks in advance.