Gear Boxes and Gear Motors are important tools for changing speed and torque output from a powered machine such as electric motors. Over time the seals can become worn and brittle. Bearings are immersed in oil and can last a long time but contaminants, leaks and excessive torque or heat can damage the bearings. The gears are also subject to damage over time. A good PM program includes periodic checks for leaks, particles in the oil and oil levels.