What was found
FLT 458 - DEN-PHL - ODOR - UPON RECEIVING AIRCRAFT, STRONG DIRTY SOCK SMELL. COMPLIED WITH JOB CARD 26L00021002. NO OIL LEAKS FOUND IN APU. CHECKED DUCT, NO LIQUIDS FOUND. REMOVED AND REPLACED AIR RECIRCULATION FILTERS PER AMM 21-21-41. NO FURTHER ODOR INCIDENTS FOLLOWED.