"Stove Polish" that is used to treat wood burning stoves to prevent rust works on brake drums without interfering with their ability to dissipate heat. It's inexpensive, easy to apply, and one application will last quite a while. It's basically atomized carbon powder and beeswax. There's plenty of it available on Ebay.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!