Tefgel
The grease Tefgel is the only solution I know of. There may be other pastes and grease type insulators. Bronze and Stainless Steel work well together, but I am not sure if Bronze and Aluminum will be any better. I'm looking at using bronze bushings for a mast issue, but haven't decided yet as I haven't had a chance to investigate. There are a couple interesting solutions for your decayed base on the board here if you search.