Try this...
Get some good motor oil and put a drop on the aluminum...
Then scrape the aluminum oxide off under the oil...
....[snip]....

I've done the very same thing except using silver-cleaning paste!
Although it's a bother, it DOES work.

I've also seen the demonstrations of the things sold at hamfests,
it appears to work very well, and the cost was not bad, either.

--Myron.
--
Five boxes preserve our freedoms: soap, ballot, witness, jury, and cartridge
PhD EE (retired). "Barbershop" tenor. CDL(PTX). W0PBV. (785) 539-4448
NRA Life Member and Certified Instructor (Home Firearm Safety, Rifle, Pistol)