As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APU HAS A HISTORY OF OIL SERVICING CURRENT OIL CONSUMPTION IS HIGHER THAN EXPECTED. GROUNDED - YES. UPON OPENING OF APU COWLING FOUND OIL LEAKING FROM THE DIFFERENTIAL PRESSURE INDICATOR, DELTA P INDICATOR WAS MISSING, WHICH CAUSE THE HIGH APU OIL CONSUMPTION. REMOVED AND REPLACED DIFFERENTIAL PRESSURE INDICATOR REF B737-900 AMM 49-91-13.