After a lot of scrubbing with degreaser and brushes (scotch brite pads makes it too shiny for my liking) I used Aluminum brightener from Napa Auto Parts with a tooth brush.Working in a very small area 3" X 3", dip the brush and scrub, then dry it off. Repeat ,repeat, repeat, rinse with water, dry, then move to the next section. Be sure to wear protective gear, goggles, gloves and clothing. This is a mild acid. The results are awesome...well worth the effort. good luck.