[Brian]

Pete, is the aluminum coated with a finish? And what are you trying to clean? Is it road tar or something like an adhesive residue, or do you want to "freshen" it up a bit.

If the aluminum is coated, I'd use nothing more than a good wax that I'd use on any automotive paint finish.

If it's NOT coated and you want to remove some kind of gunk, you may want to give acetone on soft cotton rag a try, being careful to heed all safety requirements so you don't pass out or blow yourself up, but be sure to test on a hidden area first.

If you want to "freshen" it up a bit. I'd go with a compound called Nuvite (available in a variety of grades) on a random orbit machine covered with a cotton cloth. I used my Porta Cable random orbit sander I used for woodworking, but with a foam head.

Brian