Your rear axle is a dana 35, it's smaller and weaker than a Chrysler 8.25. The C8.25 is flat on the bottom. The front is a Dana 30. All XJ's have a Dana 30. 75-90 in the front is fine don't add the friction modifier. It's only added when you have a limited slip differential. 75-140 is fine in the rear. factory is 85-90, but if you tow, or lift it. run 90-140. The rear diff cover isn't that bad. a wire brush will clean it up nice. the ID tag is between the 2 bolts on the left side. forget trying to read it. it's a thin piece of metal embossed with the diff model and gear ratio.