How do you replace gearbox oil in a Hyundai Excel 1999?

To replace the gearbox oil in a 1999 Hyundai Excel, first ensure the vehicle is on a level surface and secure it with wheel chocks. Remove the drain plug located at the bottom of the gearbox and allow the old oil to fully drain into a suitable container. Once drained, replace the drain plug and remove the fill plug, then use a pump to add the appropriate type and amount of new gearbox oil until it reaches the fill level. Finally, replace the fill plug and check for leaks.