Ask an Engineer - Oil on your Aircraft
By keeping your aircraft clean you will immediately notice any oil leaks that could indicate signs of a mechanical issue. Contact your engineer immediately and if possible take photographs of the oil leak. Once your engineer has ascertained the cause of the oil leak, remove any oil on the aircraft immediately, oil is much easier to remove when it is warmer rather then when it has cooled.
Don't mistake engine oil that may come out of the engine breather vent for an oil leak, the engine breather vent, which normally is underneath the engine, depending on your aircraft model, will sometimes vent oil mist. Always keep the breather vent clean and free of oil build up.