What was found
ON ARRIVAL TO THE AIRCRAFT FOR THE FIRST FLIGHT OF THE DAY, DETECTED A VERY STRONG OIL FUME ODOR, APU RUNNING AND BLEEDS ON. THE AIRCRAFT WAS GROUNDED. MAINTENANCE FOUND THE APU TO BE THE SOURCE OF THE ODOR AND ACCOMPLISHED WC 26L00021001. FOUND APU OIL MIXED WITH ENGINE OIL, DRAINED AND SERVICED APU OIL TWICE. REPLACED THE APU OIL FILTER, COMPLIED WITH JC 26L00021004, AND 26L00021002. NO ODOR IN CABIN IAW AMM 49-91-41.