As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
MIA - DURING CRUISE AT FLIGHT LEVEL 340 DISCOVERED CREW OXYGEN SUPPLY SHOWED ALL OXYGEN HAD LEAKED FROM CREW SUPPLY TANK. DESCENDED AND LANDED MIA WITHOUT INCIDENT. REPLACED CREW OXYGEN AND SEATED FIRST AND SECOND OBSERVER MASKS. SYSTEM GROUND CHECKED NORMAL OPERATION.