Used oil metal wear numbers from a 75W90 gear oil that I've been using in the differentials have been OK in the rear but a bit higher than I'd like to see in the front diff. I picked up some replacement gear oil that is good to -50C and which will give some protection in the viscosity range of the old SAE 90 grade gear oils when these diffs were spec'ed and is fairly well priced; Amsoil 75W-110 gear oil;
http://www.amsoil.com/storefront/svt.aspx
I'll post used oil analysis of this gear lubricant in the PF diffs after about 10K kms.
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