As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
JFK - INFLIGHT DFW-MAD. CREW REPORTED THE FIRST OFFICERS O2 MASK WOULD NOT TEST AND DEVELOPED A LEAK IN THE O2 LINE. EMERGENCY DECLARED FLIGHT DIVERTED JFK LANDED WITHOUT INCIDENT. REPLACED FIRST OFFICERS O2 MASK. SYSTEM GROUND CHECK NORMAL OPERATION.