Oil seal is the customary name of the general seal, simply the seal of the lubricating oil. It is a mechanical element used to seal grease (oil is the most common liquid material in the drive system, also refers to the general liquid material meaning). It isolates the parts that need lubrication in the transmission part from the output part, so that it will not allow lubrication. Oil leakage. Static seal and dynamic seal (usual reciprocating motion) seal is called oil seal.