Wipe any excess gear oil from the case. Step 3: Locate and remove the gear oil fill bolt. Step 4: Use a pump to slowly add the recommended type of gear oil to the differential. Step 5: Add the recommended amount of gear oil to the differential, or until gear oil starts to dribble out of the fill hole. Step 6: Reinstall and tighten the fill hole Start the engine. Shift the gear selector into the corresponding mode – “Park” or “Neutral”. Unscrew the inspection plug at the bottom of the gearbox. If the fluid leaks out of the hole, there is no need to top it up. Screw the cap back in. If nothing leaks out, this means there isn’t enough oil. .