As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WOULD NOT HOLD CABIN PRESSURE. MAINTENANCE FOUND AFT PRESSURE BULKHEAD SEAL THAT SEALS APU BLEED AIR LINE AND THE AFT PRESSURE BULKHEAD HAD FAILED. CAUSE OF FAILURE IS UNKNOWN. DATE OF SEAL MANUFACTURE, 12-29-87. SUBMITTER RECOMMENDED A MANDATORY REPLACEMENT OF THE SEAL BASED ON THE TIME IN SERVICE OF THE SEAL.