The last junction before engine power is transferred to the wheels is in your car's differential. Your car's metal ring and pinion gears are meshing against each other every time your wheels rotate. To ensure that these expensive metal components are well protected, it's important to have the differential gear oil checked and changed at recommended intervals.
Old or contaminated fluid loses its ability to protect the metal components and clutch plates in your differential. This can lead to worn or even broken ring and pinion gears, leaving your car immobile.