[ottobon100]

Typically with a failing AOS you would get suction at the oil fill tube. I got this response from another forum member after posing your question to another forum: "Likely due to combustion pressure leaking past the piston rings, if not a plugged crankcase ventilation system AOS. A compression check (dry and wet) is recommended." Another member posted: "A positive pressure at the oil filler tube would seem indicate a high pressure in the crankcase." Hope this helps.