As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: LAST 20 MINUTES OF THE FLT, STRONG "OIL" SMELL THRU THE AIRPLANE. SMELL DID GET BETTER WITH LEFT PACK OFF. UNABLE TO DETERMINE IF IT WAS THE PACK OR A BLEED SOURCE. MAINTENANCE FOUND APU TURBINE CAVITY VENT O-RINGS LEAKING. REMOVED AND REPLACED APU TURBINE CAVITY VENT O-RINGS IAW AMM 49-91-53.