Change the grease in the bearings at the intervals given in the service book. If there is not enough lubrication or it is contaminated, the bearings will quickly fail
You will need: a hex L-shaped wrench for the drain plug (usually this wrench is attached to the car in the driver's tool kit), a special wrench for unscrewing the oil filter or a large screwdriver, a funnel, a clean rag
According to the service book, the oil in the transfer case must be changed every 45,000 km