What was found
IN FLIGHT AT 41000, THE CABIN DOOR SEAL, AMBER LIGHT CAME ON. LATER THE CABIN DOOR BEGAN TO MAKE A VERY LOUD NOISE & THEN WE BEGAN TO LOSE CABIN PRESSURE. FOUND 2 CHECK VALVES WITH UPGRADED PN 9914786-1 & IN SERVICEABLE CONDITION, THE OTHER 3 ARE PN 9914171-1 WITH 1 CHECK VLV FROM RT ENG STUCK OPE. R & R 3 SERVICE AIR CHECK VALVES IAW MM CHAPTER 36-15-00 REV 44. ALL VLVS LEAK & OPS CHECKED GOOD ON THE SHIP SIDE. R & R RT ENG SERVICE AIR CHECK VALVE. REPLACED WITH VALVE. R & R TEST PORT SERVICE AIR CHECK VALVE. REPLACED GROUND SERVICE AIR CHECK VALVE. ENGINE AIR SUPPLY SIDE OF CHECK VALVES LEAK CHECKED GOOD.