The '72 outer grill surround is made of anodized aluminum. Anodizing is a process whereby aluminum is subjected to a chemical bath/electric charge. This creates a thin layer of oxidation that protects it from further corrosion. You can try to remove this coating by sanding or you can remove it with a caustic cleaner. I have heard that ez-off oven cleaner will do the job pretty easily. However, once removed, the aluminum is no longer protected from corrosion. It will polish up nicely, but will have to be frequently polished to keep it shiny. Or, you can have it re-anodized. I have read a few articles on the internet about "Home anodizing" and it doesn't look like it would be very difficult. Re-anodizing does require some nasty chemicals though.
TP
