As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
*** WHILE AIRCRAFT WAS IN FOR HEAVY CHECK *** MAINTENANCE REPORTED THE OBSERVERS OXYGEN MASK HARNESS INFLATION OPERATES ON AND OFF WHEN THE REGULATOR IS SELECTED IN EMERGENCY POSITION. MAINTENANCE REMOVED AND REPLACED THE OBSERVERS OXYGEN MASK IAW AMM 35-10-10. AIRCRAFT IS CURRENTLY STILL OUT OF SERVICE FOR HEAVY CHECK COMPLETION.