Hey, ATF is a 30wt light oil and will ruin your gear faces. The thicker the oil, the less noise and wear you will have from the gearbox. Go to an auto parts store and get a bottle of 75w90 Mobil1 and a bottle of limited slip friction modifier for the clutch. It will quiet the box and wont leak as much and will provide more power to the ground! DO NOT RUN ATF!!