is there a cover on the rear differential that requires a gasket? I need to know so I can order one cause im changing out the fluid, and im guessing if there is a gasket there then it needs to be replaced.

 

there's a drain plug in the bottom of the diff cover. Use that instead!

Make sure you have a fluid pump of some kind (I typically rig up a cheap $1 store pump squirt gun with hose and then throw it out afterwards) and heat your new oil to about 110 degrees before pouring it into the diff. (makes it much easier than trying to squeeze molassis through a straw)