As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING REMOVAL PROCEDURE FOR FWD CREW OXYGEN BOTTLE, THE AFT CREW OXYGEN BOTTLE SHUT OFF VALVE WAS FOUND TO BE FAULTY AND WOULD NOT SHUT OFF CREW OXYGEN FLOW TO THE COCKPIT. BLED OFF ALL OF THE AFT OXYGEN CYLINDER CONTENTS. REMOVED AND REPLACED AFT OXYGEN BOTTLE IAW AMM 35-11-32