225 Strange oil level behavior

Hi there,
I could not find any answers to my problem so decided to make new thread.

When i fill up oil to 5/6 level it drops down to 3/6 during first 200km and then stays that (actually for more than 1000km).
What may be the cause of it?

My firs suspect is the turbo.
Return pipe seal broke down and oil was spraying all over intake hose. It was changed.
I have too much oil in the hose before throttle valve.
Is it loosing oil through turbo untill oil level drops and return is easier?

What is your experience?

Regards,
Piotr