Oil below airbox

[Olive]

Hi all. Two days ago I went for a simple service check and as soon as the car has been placed on the bridge we saw some oil traces.
After had removed the carters we found some oil all around pieces N°5, all around direction bocal, and also a small quantity inside the carbon box, where the hose n°3 is plugged :





I called a well known specialist in France to get his opinion. It seems that CHF is not concerned. It is not sticky and not red, looks like oil (clear).
For him it is probably the hose n°3 who is dead. He also advice to change piece n°1 (oil separator).

Did you ever met this kind of trouble ? Do you have an idea ?

This hose n°3 is plugged on the airbox, I am not a specialist (far from), so could someone explain to me why is there a link with oil? What is the purpose of this hose ?

Thanks and sorry if I am not clear, a technical mail in English is not simple to write for me