i recently did a diff- autoglym engine cleaner, from halfords , is excellent stuff - also brilliant to do the enginbe bay with that, and a hose/watering can, all around the whole bay,work in with brush- rinse off - comes up brilliant and clean !
the diff- with powder coating it has to be baked in the big oven , so not sure its wise to put a diff in an oven !!!

, i painted mine black, with hammerite smooth black, tin paint, from halfords , 2 coats on there, looks good and came up new, that also is a "direct to metal/rust" paint, so no need to prep it