As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
RETURNED TO DEN DUE TO INOPERATIVE GEN & LOSS OF APU EN ROUTE. APU NO START DUE TO LOW OIL PRESSURE. APU GENERATOR HOUSING CRACKED AT 12:00 POSITION. APU SHARES OIL SYS WITH GEN. LOSS OF OIL FROM CRACKED GEN HOUSING CAUSED INSUFFICIENT OIL LEVEL IN APU RESULTING IN LOW OIL PRESSURE SHUTDOWN DURING ALTITUDE START ATTEMPT.