What was found
DUE TO CAB ALT LIGHT ILLUMINATED ON DESCENT. AIRCRAFT WOULD NOT MAINTAIN CABIN PRESSURE. RIGHT PACK ON MEL. REPLACED RIGHT PACK TCV FOR MEL. FAILED SINGLE PACK CONFIDENCE CHECK. FOUND MULTIPLE FUSELAGE DRAIN VALVES LEAKING. REPLACED 10 DRAIN VALVES. REPLACED LEFT AND RIGHT PACK BAY FLEX DUCTS AFT OF CONDITIONED AIR CHECK VALVES FOR LEAKING. LEFT AND RIGHT PACKS PASS SINGLE PACK CONFIDENCE CHECKS. AIRCRAFT OK FOR SERVICE.