From experience with aircraft (my own and others):
(1) Most important, do not use steel wool or wire brush. These will usually leave tiny steel particles embedded in the aluminum, and electrolytic corrosion will then occur at high speed. Aluminum wire brushes are good for removing really severe crusts of corrosion, but they wear out quickly and are hard to find, so aren't popular.
(2) One excellent product is Nevr-Dull, available in many auto parts shops, sporting-goods stores, hardware stores, probably Lowe's and Home Depot etc. This is the first choice for keeping aluminum airplane propellers, fuselages, and wings clean and shiny, and it seems to leave a protective coating of some kind too.
(3) If, after cleaning, you want to paint it for additional protection, first wash it with ordinary dishwashing detergent; then treat the surface with Aluma-Prep, available at auto-paint stores like English Color, and possibly at auto-parts stores; then prime it with, for example, Dupli-Color primer, and paint with the same brand of touch-up paint. I'd make it match the vehicle while I was at it. Dupli-Color paints are a really high-quality product sold at almost every auto-parts store. They are available (in spray cans) to match the color of nearly every vehicle ever sold, except motor homes.