Transmission parts’ fouling is most commonly observed in the high-mileage vehicles when they are operated intensively at high ambient temperature. Also oil can be sometimes observed on the junction of a manual transmission with an engine, on a clutch. Malfunction in transmission ventilation system can be sometimes the cause of an oil leakage too. That is why it’s better to check an air breather first, and if required to clean it.
However most commonly the cause of an oil leakage is a loss of elasticity by the oil seals or the liners because of their ageing and operating under high temperatures. The oil sealers are shriveling and adjoin to the parts loosely.
In this case impermeability of the mechanism can be restored by the help of introducing additives into an oil. The active component of this additive is a specific plasticizer. Affected by the plasticizer action the oil seals material swells and adjoin to surfaces more tightly.