What was found
STRONG ODOR RETURNED ON DESCENT. SMELLED LIKE OIL DROPPING ON SOMETHING HOT. MOST NOTICEABLE IN CENTER CABIN. ACFT GROUNDED. TROUBLESHOT AND FOUND A APU BLEED FAULT IAW TSM 25-00-00-810-823. RAN ENGINES AND APU BLEED OFF WITH NO OCCURENCE OF ODORS. FOUND APU TO BE VERY OVERSERVICED. DESERVICED OIL TO CORRECT LEVEL IAW AMM 49-90-00. CLEANED APU COMPARTMENT & INLET, REMOVED NEW AND OLD BUILDUP. RAN APU FOR HOUR. NO ODOR OR APU LEAKS NOTED, REPLACED RECITULATION FILTERS IAW AMM 21-21-41. CLEARS MDDR 55461. PLACARD REMOVED. MC NOTIFIED.