What was found
RETURNED TO DEPARTURE DUE TO CABIN PRESSURE ECAM AND RED MASTER WARNING LIGHT APPEARED, CLIMBING THROUGH FL 380. CABIN ALTITUDE WAS 10,000 AND CLIMBING WITH BOTH OUTFLOW VALVE CLOSED. DESCENDED TO 10,000. FOUND THE AFT CARGO DOOR SEAL HAD A CUT ON THE OUTSIDE. REPLACED AFT CARGO DOOR SEAL. LP 5865798