Hi Nathyluck, I think I can help as I had the same issue. (I still do) what I think you will find is a crack in the rocker cover vent pipe where it connects to the engine(on the right hand side)
It was probably caused when the air filter was changed in the past and the pipe bent upwards. The weird thing is I cannot workout how this pipe is attached, it looks like it should have a securing clip but there is not one and I am too scared to pull it any harder incase it breaks leaving a part trapped in the engine. Good news is I cleaned the whole area and it has stayed pretty oil free for the last 6 months so nothing too serious. If anyone knows how to disconnect the rocker cover breather pipe on the right hand side of the engine I would love to know.