my theory on this.at higher engine rpm more oil is present on top of engine splashing around and possibly turning to oil mist at which point this oil mist is sucked up the pcv hose into the intake manifold where in small but significant quantities it will mix with more air and fuel and easily burn off in the combustion chamber.my 300e seems to consume more oil on highway runs.i have taken care of the obvious like valve cover gasket,filler cap.plug fouling is minimal