While lubrication is an engine internal procedure, cooling and oil supply require more or less design activity on the aircraft side of the engine/airframe interface for proper engine function, depending on the engine type.
The necessity for engine cooling and oil supply provisions on the airframe can lead to interface problems because the helicopter manufacturer can influence engine related functions due to the design of corresponding oil system components.
This SAE Aerospace Information Report (AIR) deals with integration of engine oil systems with the airframe and gives information for both helicopter and engine manufacturers for a better understanding of interface requirements.