There's probably a slurry of WD-40 and corroded material inside the potentiometer. You'll need to take apart the can to clean it properly.

Also, wash off all the PCBs. There's no telling what sort of contaminants were left behind that might short things out. Once they are clean and dry, only then attempt to boot them, preferably first on the bench, rather than in-game.

The game itself is probably going to need a lot more cleaning before I'd even attempt applying or turning on power.