What was found
AIRCRAFT WAS GROUNDED: STRONG SMELL OF FUMES FROM PREFLIGHT TO LANDING. DEFINITELY IN THE FLIGHT DECK AND FLIGHT ATTENDANTS ALSO REPORTED IN THE CABIN. DURING TROUBLESHOOTING FOUND OVERALL APU AREA CONTAMINATED WITH OIL AND SOOT STAINED PRIMARILY IN THE OIL COOLER AREA, BURNED OIL SMELL AND SOME SMOKE UPON DOORS OPENING. REMOVE AND REPLACED APU OIL COOLER. PER AMM 49-91-41. OPERTIONAL CHECK GOOD. NO LEAKS NOTED.