What are the main factors that cause oil seal leakage?

The main factors that cause oil seal oil leakage:
The oil seal is not tightly sealed is the main factor causing oil leakage. When the shaft is worn and a groove is formed, even if the new oil seal is replaced, the oil seal still cannot be sealed, because the contact pressure between the oil seal lip and the shaft decreases, resulting in too little interference between the diameter of the oil seal lip and the shaft diameter after installation.

Taking the diesel engine crankshaft oil seal as an example, the main reasons for the lack of tight sealing are as follows:
①The manufacturing quality of the oil seal is poor;
②The quality of the shaft or bearing is poor;
③ Improper use and maintenance;
④ Improper installation;
⑤ Improper storage and adverse effects caused by environmental pollution.