As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: AN EMERGENCY WAS DECLARED AND THE AIRCRAFT DIVERTED TO ORD DUE TO THE FLIGHT CREW REPORTING A SLOW CREW OXYGEN LEAK - THE AIRCRAFT LANDED SAFELY AT ORD WITHOUT FURTHER INCIDENT - MAINTENANCE FOUND THE 4TH OCCUPANT 02 FULL MASK STOWAGE BOX LEAKING AND REPLACED IT PER AMM 35-12-10