A little oily residue from the solvent is normal unless you use some kind of degreaser. It is not necessary but I use carb cleaner when doing a deep cleaning ( not very often and DON"T get on plastic) You should use a good oil to wipe it down after cleaning w/ the solvent. Don't worry about the toxicity unless you plan on drinking it or become a gunsmith and clean dozens of guns a day.
"Suppose you were an idiot, and suppose you were a member of Congress, but I repeat myself." Mark Twain