I'm always looking for easier ways to clean my machines, and recently stumbled on something that actually works.
S100 works OK but it's not terrific and it costs too much. But RainX Bug and Tar Remover is not only cheap, it really cleans well: things like dirty wheels and engine cases. The instructions say to use it as a spot remover, but it's cheap enough to just use it as a general cleaner. In any case, it's nice to paintwork, but really takes care of dried-on crud.
It's not spray-on, hose off: you do have to go over it with a cloth or brush. But you don't have to scrub at all, just wipe.
Just thought I'd put it out there.