if you take the sc off dont touch the inside of it, leave it be, that black stuff is the rotor coating, and you need it there.

if you just take the sc off you will only see inside the lim, not very telling at all. if your gonna take it off 10 more bolts and your lim is off.

the sc fluid can stay in, it shouldn't leak out while flipping it over or upright. but if it needs to be changed its easy to dump it out while its off.