superclean is really aggressive. Not sure what is in it, but basically you have eched it. I tend to prefer steam cleaning(not pressure washing) and only pre soak with simple green. Amsoil metal protectant will get washed off with heavy duty cleaning, so no it would not have helped. trying it now most likely will not help either. More then likely you will need to buff the aluminum parts on a buffing wheel to restore them. You could try try a "mothers" polishing ball and some compound, then if that will not do it then buffing.

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1977 240D turbo