What was found
(AIRCRAFT NOT GROUNDED) DIRTY SOCK SMELL IN CABIN AND FLIGHT DECK ON DESCENT / PERFORMED AMM 21-00-00-615-803-B REMOVAL OF THE CONTAMINATION OF THE ECS, NO FAULTS NOTED AND NO SMELL DETECTED. THIS CLEARS MEL 21-52-01-G, CAT C, MDDR#218679 'M' PROCEDURE REVERSED, INOP PLACARD REMOVED. C/W OIL TYPE SMELL-PHASE 3 IAW ALLEGIANT AIR TC 21-000-003. NO SMELL REPRODUCED AT THIS TIME. DAMAGE FOUND WHILE PERFOMING APU BOROSCOPE INSP WO#529958 TASK CARD A32X-21-000-002. APU REPLACED AND PERFORMED TC 21-000-003.