i paid $70 (the cheapest i could find without importing from overseas) for a master system controller that's yellowed and chipped, opened it up and gave it a good once-over cleaning the contacts to get it to a good shape, and one day later it STILL stopped working 😓
just the button 1, so probably a contact issue, but jesus, i already cleaned the board... and a LOT of gunk came out of it, and the seller said it was working beforehand... ugh
this is why people just use mega drive controllers instead