Hello and welcome to justanswer.com
The fluid is a synthetic 75W 140 rear differential fluid. There is a 1/2" square drive plug on the diff case cover that needs to be removed in order to fill it with fluid. A syringe or suction type of tool is needed to do this. The fill plug is in a tight location but a short extension and ratchet normally does the trick.
I believe that the differential takes 2 liters of fluid it is a very slow drip do you think I can get 150 miles before i have real problems?