The bumper on my 1990 740 GLE is in good shape for it's age but the original color, a sort of medium brown, has faded considerably. When it's wet the color is much like what I believe to be the original but as soon as it dries it's back to the very (!!) light tan. Is there a preparation that I can apply? I tried Armoral and car wax but nothing seems to work. Thanks very much, Perk (:>)