Amsoil 75W90 Synthetic forever!
Product description: Long Life Synthetic Gear Lube SAE 75W-90 (FGR)
Specifically engineered for extended drain intervals up to 500,000 miles as set by equipment manufacturers for over-the-road trucks and heavy equipment. Prevents wear and improves equipment life. Excellent "All Season" summer and winter performance. Outperforms all conventional gear oils. Also excellent for passenger cars and trucks. Compatible with most limited-slip differentials. Performance specifications include: API GL-5 & MT-1, MIL-PRF-2105E, Dana SHAES 234 (Formerly Eaton PS-037) for 250,000 miles, Dana SHAES 256 (Formerly Eaton PS-163) for 500,000 miles, Mack GO-J & GO-J+, Meritor 0-76N, and Navistar TMS 6816 plus hypoid gear oil specifications from all domestic and foreign manufacturers such as GM, Ford and Daimler Chrysler. Can also be used in rear axles where API Service GL-4 lubricant is recommended.

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!