Has any one had experience using phosphoric acid to clean pitting on aluminum surfaces such as hard top or tower piping?

Go to your local quality paint store and pick up DuPont etch- it goes by the product name Alumiprep 33. They make the alodine for protecting after etching and rinsing the etching solution- Alumiprep 1201 (1200 is clear)
Good stuff and carries a mil-spec.
Jim