Mill Supply carries a variety of replacement 2/4 Cycle Gear Oil as well as other mower parts & accessories.

Rotary /Torco Gear Oil - SAE 85W140. 32 oz. Bottle
Gear oil for gear cases,wet chain drive units,hypoid differentials,reduction gears,ring & pinion gears,tiller transmissions.
Mower-parts.net carries replacement Gear Oil for 2 and 4 Cycle as well as other mower parts & accessories.