"YoSteve has it right here - If you're truly concerned about moisture in your engine compartment cleaning it by hand is the route. I like to use Simple Green but your results will be as good with the other degreasers/engine cleaners. One tip...in addition to your spray bottle of cleaner have a spray bottle of water available. You'll be able to localize where you put the water and if it is really a mess you'll need the extra water or you'll end up wasting your degreaser.

I can't say anymore about the PC. Just get one w/some aggressive pads. I'd suggest a few hours reading up on some of the views here, tons of great info on pads, polish/cleaners and PC techniques. "