My Sega Master System sits on the shelf unrepaired, the controller? We can fix that! Button 2 was behaving very badly so we whipped out some metho and gave it a good scrub down. You can apply this method to pretty much any controller for retro gaming.
Controllers since probably the mid-90s will tend to have carbon instead of shiny gold contacts. This highly reduces the amount of corrosion and GUNK that can get stuck and cause issues! Actually, now that I think about it, you probably could use a pencil eraser afterward as well for the perfect finish just like on cartridge pins.
Thanks go out to patrikw25 for pointing out the switch between ENG/JPN with Wonder Boy a few weeks (or even months) back now!