Unless the pins are rusty, don't use anything but a contact cleaner(like DeoxIT) on them. The discoloration is from heat(not oxidation) and will not affect conductance. Scratching the pins, with any kind of abrasive, or metal bristles(outside of brass or copper), will encourage the oxidation of steel pins. Good stuff: (http://store.caig.com/s.nl/sc.2/category.188/.f) or higher temp (http://store.caig.com/s.nl/sc.2/category.279/.f)