What was found
LOG PAGE 37837. ON TAKEOFF ALL NORMAL, THEN NR 3 ENGINE OIL PRESSURE WENT TO 65 PSI CONSTANT. RETURNED TO MIAMI, DID NOT SHUT DOWN ENGINE AND NO EMERGENCY DECLARED. CANCELLED FLIGHT. FOUND O-RING ON PRESSURE RELIEF VALVE DAMAGED, REPLACED O-RING. AS PRECAUTION, REPLACED PRESSURE RELIEF VALVE PER MM 79-32-0. P/N 626447. OPS CHECK ON RUN-UP OK PER MM 71-00-0. RETURNED AIRCRAFT TO SERVICE. (X)