As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CREW MADE AN AIR TURN BACK TO DEN DUE TO CABIN EXCEEDING 10,000' PRESSURE THROUGH FL230. MAINTENANCE REMOVED AND REPLACED THE AFT CARGO DOOR SEAL AND INSTALLED NEW SEAL IAW AMM 52-32-18 PB 401 AND PERFORMED PRESSURIZATION LEAK CHECK IAW AMM 05-53-00 PB 401.