The Oil Breather.
The oil Breather comes from below the dip stick to the Air input pipe to the turbo. This is after the Air Filter.
This should be taken off periodically and checked for a clear path, by blowing into it. If this is blocked then it must be replaced.
Where the breather is fitted into the air input pipe. [Shown just below the red arrow] This fitting has a bayonet connection. This has a habit of loosening itself and allowing the filtered air to the turbo to be exposed to the elements. Contamination can destroy the turbo.
Cure, ensure the connection is tight by turning a quarter of a turn. Then using a tie clip, secure the oil breather pipe to ensure the engine vibration does not allow it to loosen up again. Without support this pipe vibrates quite a lot.