As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APPROXIMATELY TWO HOURS INTO FLIGHT, THE CREW NOTICED THEIR OXYGEN INDICATED 10PSI WHEN DONNING MASK FOR BATHROOM BREAK. RETURNED TO DEPARTURE. SUSPECT CAPTAIN'S OXYGEN BOX TEST SWITCH MAY HAVE STUCK PARTIALLY OPEN BUT COULD NOT DUPLICATE. REPLACED CREW O2 BOTTLE AND LEAK CHECKED ALL 4 CREW O2 BOXES AND LINES.