I just changed the rear diff fluid. Used Mobil 1 75-90W LS (LS for Limited Slip Additive). The Mobil 1 already has it added. I also added 7 oz of limited slip additive as well, can't hurt. Including the LS additive it took about 3 qts. and 4-7 oz, give or take, to fill it back up.
When you take the drain plugs out clean the swarf off of them and then spray them down with brake clean and wipe them down with a rag. You will also need thread sealant that you apply to the threads on the plugs before re-installing. Leave the first thread (one going in the hole) clean and smear a thin layer around the rest of the plug. Tq. is 22 ft lbs (if I remember correctly, check that though).