Its kinda like acetone but it wont harm anything. It breaks up the oil, making it easier to get off..You still need a scrub brush a towel, and an air compressor to get em totally clean..
Take apart your diffs, and soak everything (not the diff case, or the o-rings) in the Naptha..take out the parts one piece at a time, and scrub em with the brush, or wipe them off, then blast with air, careful not to lose the little shims!..Clean out the diff case with Q-tips, and Naptha, wipe it all off, blow it out..maybe replace the bearings and the o-rings while you are at it..It's always a good idea when you clean your diffs to rebuild them also..New bearings, new O-rings..you'll have smooth diffs always, and no leaks from shot o-rings