simple water dunking my displace all the inpregnated oils from the pores of the aluminim covers there probly made out of machined 2024 t6.de grease them from all preaveus polishes you have tryed. dunk them for a couple of days in a tub of water with about 4 shot gasses of bleach it should disapate the staines if not you will have to boil them in the same solution.
Several coats of Simple Green and letting it set cleans aluminum well....but don't leave wet too long. I soaked some parts over night and it turned them black.
its true it dose corrode the metal to an extent thats why its duluted so much. it will ech the metal an even yellowish color an it can be buffed back to normal from there with mothers mag and aluminum polish.
