How do I change and fill up My Polaris Express 400 gearbox oil?

To change the gearbox oil in your Polaris Express 400, first, ensure the vehicle is on a level surface and turn off the engine. Remove the drain plug and allow the old oil to fully drain out. Once drained, replace the plug and refill the gearbox with the appropriate oil using the fill plug, checking the level with a dipstick or by sight until it reaches the recommended level. Finally, run the engine briefly to circulate the new oil, then recheck the level and adjust if necessary.