Well as far as controllers go the best you can hope for is to clean both the rubber tops and bottoms, and where they contact with the board with high proof isopropyl alcohol and hope for the best, otherwise, find replacement rubbers or controllers. I really don't recall what an old Genesis weighs (been 10+years) so I had no idea if that was good or not. $50 for a non TMSS genesis seems to be pretty damn good when you factor in the added controller and game.

I don't remember well, but other than Street Fighter II I don't think too many games used a 6 button controller anyway, and I already have that on SNES.

Perhaps just buy it and be done with it, as trying to find one as pretty as that is probably waiting for disaster or really dumb luck.