Axial play, how much is normal?

What exactly would i be looking for? You mention face wear of the axle C-locks, would this be obvious for a axle novice like myself to spot?

I've never taken the cover off of a rearend before (axle that is LOL) so this might be a stupid question, if i take the cover off, all the fluid will come out, how do you refill it when the cover is back on, i assume there is a filler hole at the top or something?

When the cover has come off, is there a gasket that needs to be replaced?