The Valvoline Web site says that Valvoline full synthethic gear oil is OK all all limited slip differentials. I've always used this gear oil; however, as you all know, the LS diffs in Xterras say "Use on LSD Oil."

Do you think it's OK to use the Valvoline in my Xterra? I strongly prefer it.

And yes, I already have some rear diff gear whine that been's reported by many members of this forum. I'm assuming the Valvo full syn gear oil might help this.

The Valvoline is fine for front and rear differentials. That's actually what I have in mine right now. All Nissan is requesting for LSD oil is that it has LSD friction modifiers. The Valvoline already has them so you don't need to add more. Any gear oil that has them will clearly state on the bottle that it is "for use in LSD aplications" or will say "Includes LSD modifiers" or something along those lines. If they don't have the modifier they will usually say something like "for use in LSD applications as a top off oil only."

Since the Valvoline is a lighter weight than factory you'll probably actually have more hum from the diff. when cold but possibly less when warm. Mine makes a lot of noise for the first couple minutes of driving when the temps drop below about 40 degrees. This has been the case with all the 75W-90 GL-5 synthetics, but not so much with 80W-90 GL-5 gear oils.