AN A320 FLIGHT CREW REPORTS OF INADEQUATE MAINT TROUBLESHOOTING OF A CONTINUING CREW OXYGEN LEAK AND MAKING INCORRECT DEFERRALS TO DISPATCH ACFT.

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ACFT ARRIVED 1.5 HRS LATE FROM ZZZ1 WITH OXYGEN ECAM PSI GAUGE DEFERRAL/WRITE-UP SAID BOTTLE PSI AND ECAM PSI WERE DIFFERENT. ECAM OXYGEN PSI GAUGE INOP. ACFT LEFT ZZZ1 1850 PSI ARRIVED ZZZ2 1300 PSI ON BOTH ECAM AND BOTTLE. THERE WAS OBVIOUSLY A SERIOUS OXYGEN LEAK THAT HAS BEEN GOING ON FOR DAYS. PREVIOUSLY WRITTEN UP AS REPEAT ITEM OXYGEN LOW. ZZZ2 MAINT RELEASED THE AIRPLANE KNOWING IT HAD LEAKED 550 LBS OF PURE OXYGEN ON ITS FLT FROM ZZZ1. WHEN I FINALLY FOUND A ZZZ2 MECH; HE SIMPLY SAID; 'CAPT; WHAT DO I HAVE TO DO TO GET THE AIRPLANE OUT OF HERE.' GENTLEMAN AN OXYGEN LEAK PROBABLY IN THE AVIONICS COMPARTMENT/NOSE GEAR WELL IS VERY SERIOUS. LOTS OF GREASE AND SPARKS. ANYONE REMEMBER THE NASA GEMINI EXPLOSION ON THE PAD? FLT WAS CANCELED. FIRST WRITE-UP OF THE DAY IN THE NEXT MORNING; LOW OXYGEN PSI 820 PSI. ACTION: TIGHTEN CLAMP ON WATER HEATER. WHAT IS GOING ON HERE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: REPORTER STATED THIS ACFT HAD FLOWN FOR SEVERAL DAYS WITH A CONTINUING CREW OXYGEN LEAK. ALL THE CREW MASKS HAD BEEN REPLACED; BUT THE OXYGEN LEAK CONTINUED. THE DEFERRAL OF THE LOWER ECAM CREW OXY PSI INDICATION WAS INCORRECT AND DID NOT ADDRESS THE ISSUE THAT THE CREW OXY BOTTLE DIRECT READING PRESSURE GAGES AND THE ECAM PAGE PSI INDICATION READINGS WERE THE SAME. HE DOESN'T KNOW IF ANYONE IN MAINT DID A SPECIFIC PROCEDURE TO LOCATE LEAKING OXYGEN ON THE LINES AND FITTINGS IN THE AVIONICS COMPARTMENT. REPORTER ALSO STATES HE HAS SERIOUS CONCERNS ABOUT INADEQUATE MAINT TROUBLESHOOTING ALONG WITH USING INCORRECT MEL DEFERRALS TO GET THE PLANE OUT OF TOWN.