What was found
CLIMBING THROUGH FL242 CABIN ALT WARN HORN. CABIN ALT OBSERV CLIMB THROUGH 10000 AND AIRCRAFT LEVELED. DESCENT BEGAN AND CABIN ALT CLIMBED TO 13500, NO HELP IN STBY OR MAN, PRESS MODE OUTFLW VLV FULLY CLOSED AND FWD VALVE CLOSED LIGHT ON ENTIRE TIME. CHECKED ENTRY SERVICE CARGO DOOR SEALS. FOUND WORN FWD CARGO DOOR SEAL. REPLACED FWD CARGO DOOR SEAL. PRESSURIZED A/C, ALL IND GOOD, NO LEAKS.