I have outright washed multiple monitor chassis (flyback and all, psychotic as that sounds), a Defender power supply board, and some other game boards which have been I think an MK2, 2 de-cased Sega NAOMIs, a Space Invaders Deluxe and probably some other stuff I can't remember off hand with... some dollar store Simple Green and a water sprayer. you just have to pull all socketed items like roms or security chips or bios chips, and the backup battery.
I have kind of an advantage, doing these at work with a sprayer in our kitchen and those bathroom blow dryers for drying the boards. everything's worked for me, so I don't see any major issue with my crazy approach.
one exception though, I will not do this to a Capcom CPS2 board, the kind that have those "suicide batteries" because I don't want to discharge any of that circuitry in the water. those you're just kind of relegated to a toothbrush I guess. sucks, I know, but you're kinda stuck unless you have Phoenix roms on those.
but anyway, spray it with the Simple Green everywhere, rinse it thoroughly, then dry it however you see fit to the best of your ability. you can finish it off with sun heat, a fan, a heater or whatever. exercise the same kind of PCB handling precautions, though, doesn't that kind of go out the window by doing this?
this I've found is way better than rubbing alcohol. rubbing alcohol somehow makes the surfaces you wash sticky.. this stuff gets EVERYTHING off.
people may think I'm crazy, but there's some other strangelings on here that throw them in dishwashers....