Construction of an Oil Seal
The basic principle of sealing is straightforward – the flexible lip is held against the rotating part (usually the shaft) whilst the casing (or O.D.) is pressed into the housing or bore and holds the seal in place. The sealing lip needs some form of lubrication to avoid overheating and is usually energized by means of a garter spring.
Update: Leakage-free
Passenger cars

When it comes to replacing spark plugs in your car, cost is always a factor to consider. New spark plugs can vary in price depending on the brand, material, and quality. It is important to understand the factors that contribute to the cost of spark plugs in order to make an informed decision.
An outer case, a body made of metal or provided with a rubber layer

wheel oil seal. Signs of a faulty wheel oil seal include oil leakage from the wheel hub, unusual noise coming from the wheel assembly, and excessive play or wobbling of the wheel. If any of these symptoms are noticed, it is important to have the wheel oil seals replaced immediately to prevent further damage to the wheel bearings.
Oil seals go by many names, such as shaft seals, dirt seals, grease seals, lip seals, and many other variations of these. They are essentially simple devices used in rotary shaft equipment to prevent lubricant from escaping and for excluding contaminants such as dust, dirt and water. An oil seal’s most important function, however, is that it protects every type of ball, sleeve and roller bearing in the rotating shafts. The seals also prevent the integration of two different fluids that shouldn’t mix, such as oil and water.