Re: Rear end
Normally 4 ounces in the rear diff should be enough. Sometimes an already pre-mixed lubricant is used, but its known that it can have not enough friction modifier. So good to know first what they used, before pooring the total amount of 4 ounces in. If the diff is full, you will need to drain some fluid, before you can add the modifier.
After adding the modifier, you will need to do tight figure 8 turns on some empty parking lot or any other suitable space, so that the modifier will be mixed and taken inside the Vari-Lok. It will prevent full lock of the vari-Lok, which is necessary when making (tight) turns and both wheels on the same axle will have different speeds.