What was found
CABIN BROKE AT 21,000 FEET IN AUTO MODE. TRIED MANUAL AND FOUND UNSUCCESSFUL. DESCENDED TO 11,000 FEET AND WAS THROUGH 14,000 FEET BEFORE THE PASSENGER OXYGEN MASKS DROPPED, MEL 21-30-1C. OUTFLOW VALVES LOCKED OPEN. LAX SECURED LOOSE SECTION OF CARGO DOOR SEAL AT LOWER CORNER AND RESTORED OUTFLOW FLOW VALVES TO NORMAL CONFIGURATION, OPS CHECKS GOOD.