Not sure if this was suggested to me here or from someone else where but the easiest way I have found to clean white walls is with a damp magic eraser. In a few minutes it took all of the scuff marks off. Found generic ones that I can get in bulk on Amazon that do the job well. Actually my kids washed the car last.

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I have found that having an old car is a constant project that is never done. I think that is a good thing. Keeps me learning new things. Having two from different eras is just a form of higher education.