Finally got an answer back from Valvoline:
can't be too carefull!
Product Information A PRODUCT OF THE VALVOLINE COMPANY A DIVISION OF ASHLAND INC. VALVOLINE HIGH PERFORMANCE GEAR OIL Valvoline High Performance Gear Oils are superior sulfur-phosphorus, extreme pressure gear lubricants formulated with premium quality basestocks to meet the demands for excellent performance. It is designed to provide excellent load carrying capacity, extreme pressure properties, anti-foam performance, demulsibility, corrosion protection, thermal stability protection, and service fill limited slip capability. These products are recommended for conventional rear axles, limited slip rear axles, and transmissions requiring EP gear lubes under high speed, high load, high torque, and high horsepower conditions. Valvoline High Performance Gear Oils meet or exceed: Ford M2C108C; Mack GO-H, & GO-J; Mil-PRF-2105E; API Services GL-5, GL-4. The Valvoline High Performance Gear Oils Advantages: Thermal Protection: Provides outstanding thermal stability for cleanliness and longer service life. Wear Protection: Contains additives to assist in protecting gear teeth against pitting, spalling, and scouring. Reduces Chattering: Contains special additives to reduce chattering in limited-slip differentials. Corrosion Protection: Protects parts from rust and corrosion. Approvals/Performance Levels Viscosity Grade/Other MIL-PRF-2105E - - - - - -, 80W-90, 85W-140 API GL-4 75W-90, 80W-90, 85W-140 API GL-5 75W-90, 80W-90, 85W-140 FORD M2C108C - - - - - -, 80W-90, 85W-140 API MT-1 75W-90, 80W-90, 85W-140 Test 75W-90 80W-90 85W-140 Vis @ 100C (cSt) 15.5 14.5 26.7 Vis @ 40C (cSt) 86.91 141 361 Viscosity Index 190 98 99 Spec Gravity @ 60F 0.887 0.900 0.904 Density (lbs/gal) 7.39 7.49 7.53 Brookfield Vis., cP 140,000(-40C) 125,000(-26C) 120,000(-12C) Pour Point, C -39 -27 -15 This information only applies to products manufactured in the following location(s): USA, Canada. Effective Date: Replaces: Author's Initials: Code 07/08/03 07/29/98 DJD