What was found
TWENTY MINUTES AFTER TAKE OFF, LEVEL 1 "HYD 3 ELEV OFF" CHECKED QRH. ALSO NOTED A STEADY REDUCTION IN HYD 3 QTY, RETURNED TO DEPARTURE. ENROUTE, LEVEL 1"HYD 3 FAIL", COMPLIED WITH QRH AND LANDED. FOUND NR 3 HYD SYS PRESSURE TRANSDUCER (APTE-150-5000G) LOOSE AND O-RING CRACKED. REPLACED O-RING IAW MM 32-47-01-4 AND TIGHTENED BRAKE PRESSURE TRANSDUCER. SERVICED NR 3 HYD SYSTEM TO FULL REF MM 12-13-02-3. LEAK AND OPS CHECK GOOD. ACFT OK FOR SERVICE.