If your tractor hydraulics uses a common sump with the the rear axle, you should not use an AW series oil. It's strictly a hydraulic oil that won't do the gearing any good. You need a UTF type oil (Universal Tractor Fluid). You owners manual should specify the oil in the rear axle/hydraulics and the transmission. They are often the same type oil.
The AW series are strictly hydraulic oils used in "pure" ( not drive gears or transmissions) hydraulic systems