How a Oil seal works in a system? Which is the best oil seal to be used in a Automobile?

An oil seal functions to seal a moving shaft, sealing lubricants in and contaminants out. The sealing lip is made of rubber, neoprene, Viton, or some other flexible, durable material. The inside diameter is slightly smaller than the part that it seals thereby making a positive seal. Some seals use a spring to assist this. The best seal for automotive use is probably the seal that the car was equipped with.