Call me old-school but I can't picture using Simple Green for cleaning moving parts. It's not simple, due to the need to avoid contamination, and it's not green, because the rinse water is contaminated by petrochemicals anyway, and fresh water is no longer an infinitely renewable resource in all parts of the country. For leaning a cassette on the bike I think WD-40 is fine - enough kerosene in it to loosen things up, but mineral spirits will work a bit better. I would spray it, let it sit for a while, brush with a bit more solvent and then clean off with a shop rag or similar (the mop suggestion looks good).