Reserved for some useful links...
3 Button Rubber Pads https://www.mortoffgames.com/controller-repair-parts215/sega-genesis-3-button-controller-conductive-pad-set
6 Button Rubber Pads https://www.mortoffgames.com/controller-repair-parts215?product_id=938
Youtube Videos on Cleaning
1. https://www.youtube.com/watch?v=XdJK6IBnfeU
2. https://www.youtube.com/watch?v=Jhf6EDgVmkk
3. https://www.youtube.com/watch?v=2ltuwD9MryY
4. https://www.youtube.com/watch?v=KiICFn2vz88