* Age and Wear: This is the most common cause. Rubber seals degrade over time due to exposure to oil, heat, and the constant vibration of the engine. Hardening and cracking are typical signs of age, leading to leaks.
* Improper Installation: If the seal was ever replaced, incorrect installation is a significant possibility. This could involve damage to the seal during fitting, improper seating in the crankcase, or insufficient lubrication.
* Crankshaft Damage: A scored or worn crankshaft will prevent the seal from making a proper seal. This damage could be caused by corrosion, lack of lubrication, or excessive wear.
* Oil Pressure: Excessively high oil pressure can force oil past a seal, even if it's otherwise in good condition. However, this is less likely to be the *sole* cause of a leak, usually compounding an existing problem.
* Misalignment: Misalignment of the crankshaft or related components can put undue stress on the seal, leading to premature failure. This might be caused by previous engine work or damage from an accident.
* Vibrations: Excessive engine vibration, perhaps from worn engine mounts, could contribute to seal failure by repeatedly stressing the seal.
* Improper Seal Type: Although less common, using the wrong type of seal during a replacement could lead to leaks.
To diagnose the specific cause, a mechanic would need to inspect the seal and surrounding components. They might check for crankshaft wear, assess the seal's condition, examine the installation, and even measure oil pressure. Simply replacing the seal without addressing the underlying cause will likely lead to another leak soon after.
