What is the function of the oil seal?

Engine: Crankshaft--Crankshaft front and rear oil seal valves--Valve oil seal (engine repair kit o-ring) (distributor oil seal, water pump oil seal, balance shaft oil seal, oil pump oil seal...); Camshaft--camshaft oil seal ; Transmission: transmission--transmission front and rear oil seal shift lever oil seal (transmission repair kit o-ring) (transfer case--transfer case front and rear oil seal); rear axle: half shaft--rear half shaft oil seal poor Speed gear-(front) rear angle vector oil seal, rear wheel oil seal, front wheel oil seal, direction engine oil seal (steering gear repair kit o-ring), direction booster oil seal (front axle oil seal).

All parts that have liquid lubricating oil in the running body box and are connected to the outside need oil seals. Some are rubber, some are metal, and most are steel-bonded rubber, such as the crankshaft rear oil seal, the front and rear oil seals of the gearbox, the left and right half shaft oil seals, the front oil seals of the final drive, the air compressor crankshaft oil seals, etc.