| *IF* the half-moon is leaking as you say, it is *NOT* the half-moon plug. If the pressure from boost is escaping through the half-moon, then the boost-pressure is going into the crankcase. (Surprised it hasn't launched your oil dipstick yet) One or both of your PCVs is likely stuck open. (The PCV is supposed to close when hit with positive (boost) pressure so it doesn't go into the crankcase)
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