Do not, I repeat "DO NOT" use a degreaser or anything like SuperClean on bare aluminum or it is going to end up a white chalky mess.
Luke butre said, use gas and a stiff plastic brush like a toothbrush. Then spray it down with soap and water. If you have a little gunk left over, take it to a hand car wash and pressure wash it after you have all of the gas residue rinsed off.