Originally Posted By: wings&wheels
Do the diffs have any yellow metals? There is a concern w/ GL5 lubricants and yellow metal corrosion at high temps. I would look for a GL4 conventional or, if you want the benefits of a syn, look for one that indicates the use of non-corrosive additives such as Redline (which I run in my old Land Rover diffs after talking to their tech desk). Check w/ the manufacturers.
If he does need a conventional GL-4 oil, NAPA sells Sta-lube 85w90 GL-4.