Being in the hvac biz,there are 2 types of coil cleaners.
The acid type will only work on fairly clean aluminum and it will brighiten it up.
What you want is a non acid,foaming alkaline type cleaner which contains Sodium Hydroxide aka LYE. These are used for general cleaning of dirt,grime,oily gunk removal.Ask for some Renuz or for SERRIOUS cleaning,Black Max. Use rubber gloves and saftey glass's cause this stuff DON'T play.
Issue will be how much Maginesium is in the Aluminum cause it WILL turn it BLACK if it has a high mag content.
You can try some Mag wheel cleaner as well or even some Easy Off oven cleaner.
I use both when cleaning,etching my aluminum panels. Each will give true aluminum a different color finish. Acid is bright,Alkaline is a touch darker.
If you look at the trans tunnel junction right below the shifter,you'll see the difference between acid,front and alkaline,back and also matches the shifter cover. Yeah it's a Chebell and the owner wanter it that way,but ther IS a difference in how each chem reacts with the aluminum.