Is there a special method to clean it? I tried some brasso, but it didn't seem to do very well. I also tried a wire brush wheel and that was not much better.

If I did a patch, would the shim stock need to be brass Also?

1947 First Series Chevy 2 ton COE
2005 - It started in the Gallery
2023 - Follow the restoration in my Project Journal
1962 IH Scout 80
1982 Chevy Caprice Classic