10secDodge

I work with aluminum castings for a living. It is not uncommon for aluminum components to oxidize since the are only shot blast from the manufacturer. Any moisture at all will cause this. On my race car manifold or valve covers I polish them in the winter months and keep them wiped down. When it is damp out the condensation will cause it. FWIW, both my cars sit in a heated garage and I still have to keep an eye on it.