Just clean the mating surfaces that’s what matters more. The part the connects to the terminal and the part that connects the wiring. The rest is just aesthetic purposes, but I would go at it with a wire brush. Other options are scotch pad, back of a sponge (the green part), maybe some 600 grit sandpaper if it’s really stuck on thereIt looks like it's bolted together and sealed, is that right?
I cleaned everything and it looks brand new now. I'm just wondering if it's sealed then I don't have to take it apart to clean it further...?