[kyguy]

Any advice about this vehicle is appreciated. Just bought a Beauty 1999 Grand Cherokee with Quadra Trac . Need to service the Front and Rear Diffrentials. Owners Manual says 75-140 Full Synthetic Gear Lube. and a Limited Slip Diffrential Addative. What is the best 75-140 Synthetic for this. I have used Valvoline is that OK. For the Addative Amazon has
Genuine Mopar Fluid 4318060AC Limited Slip Additive - 4 oz. Bottle for $10 is that what is required.

 

[Mr. Mike]

Sounds like a plan to me. You'll also need synthetic oil resistant RTV sealer for the differential covers.
Replacement cover bolts if yours excessively rusted good idea.
Considering the labor involved cleaning stock covers, aftermarket bling covers a thought.
Besides viscousity check the API specifications of the lubricant.
Goes w/o saying quality jack and stands on solid surface before crawling under.