The best way to clean contacts that I have found without harming them is to use the NES cleaning past that Nintendorepairshop.com uses. This stuff is great, I got my Sega CD contacts to where I don't have to reinsert it at times into the Genesis to work. I also fully restored NES, SNES carts that had green corrosion on the contacts that wouldn't power up at all. This stuff is really good, 1 bottle is enough to clean over 100 carts.