I find Meguiars NXT All Metal Polish very good, £7 from your local Halfrauds.
The blurb, NXT Generation® All Metal Polysh cleans, polishes, and protects all wheels, stainless steel exhausts, chrome air intakes and valve covers, aluminum, brass, copper, silver, and all other bright work components. Meguiar’s Microscopic Diminishing Abrasive Technology (MDAT) removes built-up oxidation, tarnishing, and staining faster and safer than traditional harsh abrasives.
Darren