What was found
(CAN) ENROUTE AT 7000 FT, ACFT STARTED TO NOD UNCHARACTERISTICALLY. IT WAS NOTED THAT THE NR 1 HYD SYS PRESSURE WAS HIGH (IN THE RED). DECISION TO RETURN MADE AND NR 1 HYD SYS DE-SELECTED BUT PRESSURE REMAINED HIGH. NO OTHER ADVISORY/CAUTION LIGHTS WERE ON AT THIS POINT. ABOUT 10 MINUTES AWAY FROM DESTINATION, PRESSURE DROPPED AND "HYD NR 1 RESEV LOW" LIGHT CAME ON FOLLOWED BY M/R AND T/R SERVO NR 1 PRESS, HYD NR 1 PUMP FAIL, PSAS PRESS AND AUTO-PILOT FAIL LIGHTS. EMERGENCY CHECKLIST CONSULTED AND CARRIED OUT. ACFT LANDED AND SHUTDOWN WITH NO FURTHER INCIDENT. PAX WERE BRIEFED IN-FLT AND AT SHUTDOWN. THE HYD NR 1 SIDE OF THE RT HEAT EXCHANGER FOUND TO HAVE CRACK AT BOTTOM OF HSG. NR 1 HYD SYS DRAINED OUT ALL OIL. HEAT EXCHANGER REPLACED. GROUND RUN LEAK CHECK C/W. NO FAULTS.