During Maintenance Inspection on an A320 aircraft; it was reported that the Crew O2 Bottle Service Port Cap was loose and not sealing.

Narrative

During Crew O2 bottle shut off valve safety wire inspection; it was noted that the Crew O2 bottle service port cap was loose and not seated/sealing. The security of the cap (tight/ sealed) is an aircraft safety item. If the service port (internal) check valve fails; the only remaining protection to stop 100 percent oxygen (tank) from discharging into the aircraft is the service port cap!!! A non-seated/ sealed cap (like this occurrence) would have the same end effect; as not having a cap installed at all.There is no CDL relief for a missing cap (no-go item with a missing cap). 100% oxygen discharge into cabin could be an extreme fire/ explosive hazard under some circumstances. Additionally; if the Crew O2 bottle inadvertently discharges during flight; there will not be oxygen available for the flight crew to perform their duties during event. Another scenario is with an oxygen tank low pressure/ no pressure condition; could cause the Flight Crew to divert the flight.Recommend:1) Maintenance Training2) Maintenance Bulletin3) Technician Crew Briefing Item