I've fixed many NES controllers and system by just replacing the connector or rubberpads under the buttons. I also know that there are rubberpads for SNES controller and you can replace the N64 joystick.

What I want to know is that are there any other repair parts for older machines? Has someone found rubber replacement pads for Sega Master System or GameBoys for example? How about replacement cartridge connectors for Sega systems?