What was found
WITH APU ON BOTH ENGS SHUTDOWN, APPROX 20 MINUTES IN LINE, CABIN & COCKPIT FILLED WITH POSSIBLE TOXIC FUMES, DIRTY SOCK SMELL. CAPTAIN NOTICED IRRITATION OF THROAT & BRONCHIA. ACFT RETURNED TO THE GATE. COMPLIED WITH JOB CARD 26L00021001 & 26L00021002. DETERMINED APU TO BE SOURCE OF ODOR, REPLACED LEAKING APU SEALS. ACCOMPLISHED APU & COMPARTMENT WASH & CLEANING. COMPLIED WITH ECS DECONTAMINATION IAW JOB CARD 26L00021001. NO ODOR PRESENT.