As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHILE AT CRUISE 330 CABIN PRESSURE WAS SLOWLY LOST AND MASKS DROPPED. REGAINED CABIN PRESSURE CONTROL AT 250. A/C FERRY TO MKE. REPACKED ALL O2 MASKS, GROUND PRESSURIZED A/C. COULD NOT DUPLICATE PROBLEM. PERFORMED EVALUATION FLIGHT. NO AUTO PRESSURIZATION PROBLEMS REPORTED. AIRCRAFT RETURNED TO SERVICE.