You might want to check that cap to make sure that air can get through it easily, its a coallesing cap so its supposed to have a mesh screen in it to stop oil vapor from going out., yet it needs to let air in while driving in order to vent out the draft tube. if that is plugged you can get negative pressure in the crankcase and may lose oil out the draft tube. And when the engine shuts down it should breathe just the opposite way, up the draft tube and out the cap.