I just cleaned my BB valve covers. They are decent driver quality but the factory chrome was poor. In the grooves at the bolt holes there is very little chrome, platers call it a shadow where it does not plat correctly because of the shape. I used paper towels soaked in white vinegar . Laid them in place about a day or two and it removed almost all traces of the rust down to bare metal. I scrubbed it with cleaner and a stiff brush. Then I dabbed a little aluminum paint where it was bare and blended it and they don't look too bad. Guess I will see how long to lasts.