The plug is exactly what the name describes, so if there is a constant leak out of it, it has to be the BS007 o-ring on it that’s gone but this is very unlikely (as its not a o-ring that’s worked in the cycling of the marker) not impossible however it may have a nick in it. If it’s not a constant leak and only happens whilst you’re firing the solenoid does exhaust excess pressure to the left hand side of the grip frame, which can be felt as a draft on your right hand whilst shooting left handed.