Motul's Gear 300 75W-90 is a fully synthetic ester gear oil, built on the Ester Core base and fortified with extreme-pressure additives for racing gearboxes and differentials. It is intended for gearboxes, transaxles, transfer boxes and hypoid axles in sports and high-performance road cars. This 20-liter orange jerry can is the bulk size for shops, track teams, and enthusiasts who service several units. Its specification sheet lists API GL-4 and GL-5 and MIL-L-2105D compliance. Choose it over a generic gear oil when you want a shear-stable fluid for heavy-duty track or rally use, since the manufacturer says the oil forms an unshearable oil film even in extreme conditions. It also stays in viscosity grade 90 after the KRL 20-hour shear test, per the SAE J306 method.
Stock or budget fluids are a poor fit for repeated heat cycles, and this formula is built to resist that breakdown. The manufacturer reports reduced friction and wear, and it describes a fluid that stays fluid at low temperature to allow easier gear shifting when the gearbox is cold. Owners on user forums describe smoother shifting after switching to it, with one reporting it on a Subaru rear differential and five-speed box. Fitment is the critical check: this standard version is for units without a limited-slip system, and the manufacturer's Gear 300 LS 75W-90 is the separate option for limited-slip differentials. Long-tail searches this covers include 75W-90 synthetic ester gear oil 20L, non-LSD differential fluid, MIL-L-2105D racing gear oil, and track manual transmission fluid.
The manufacturer positions this standard version for units without a limited-slip system and points LSD buyers to Gear 300 LS 75W-90, which contains a friction modifier for limited-slip units. Owners on user forums say they run a separate fill when servicing an LSD, so confirm the correct variant before ordering.
User forums report that the 75W-90 fluid works for differentials and transfer cases, but an automatic transmission calls for its own fluid. Owners on user forums say a Subaru five-speed automatic required a different fluid, so check your service manual first.
Owners on user forums say the sweet ester odor is normal and lingers in the garage, and that the oil should not leak if the seals are sound.
Draining and refilling a differential or manual gearbox is a manageable DIY job for owners comfortable with a fluid pump and a torque wrench. Owners on user forums say the fluid is easier to drain when the unit is warm, and they treat each differential as its own fill, since front and rear capacities differ. The owner's manual is the reference for fill capacity, so confirm it before you buy the 20-liter size. Cars with limited-slip units need the Gear 300 LS variant, as noted above.
