When dealing with aluminum, the paint isn't as important as the prep and the primers. Sure you want a paint that's going to keep its shine for many years, but the paint won't hold down the oxidation. The best way to clean up aluminum is to sand plastic the corrosion and use an epoxy primer asap. I use all Basf products. Ep569 is a great epoxy primer. I understand that it may not be practical to remove the davit to sandblast but that is the best way. If you are going to clean it up with out removing use a stainless steel wire brush or 3m "cookie wheel" lol not sure of the technical name but I know they are orange. Get aggressive with it till all the black dots are gone and clean with a degreaser and a clean rag. It you put a filler on it to fill the voids do so on top of the primer and re prime before paint. Good luck hope it works out for you. Pete