ACR MAINT PERSONNEL RELEASED A B767 FOR A TRANS-ATLANTIC FLT FROM A FOREIGN COUNTRY TO THE UNITED STATES OF AMERICA WITH A HYD PRESSURE LEAK NOTED IN THE ACFT LOGBOOK WHICH COULD NOT BE FOUND OR CORRECTED. THE FLC DEPARTED WITH ALTERNATE ARPTS PROPOSED IF MORE TROUBLE DEVELOPED. THE ACFT ARRIVED WITH A LOSS OF SYS FLUID IN ALL SYS; HARDLY ADEQUATE; FOR CTL OF THE ACFT FOR BOTH LNDG AND TAXIING TO THE GATE. CAPT VETOED FO REQUEST FOR PRECAUTIONARY LNDG.

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I WAS FO BACKUP ON JUN/XX/97; FROM FRA TO ORD. ON ARR AT THE ACFT FRA MAINT WAS WORKING ON THE PLANE. THE INBOUND CREW RPTED A LOSS OF FLUID FROM THE CTR HYD SYS. AFTER WORKING ON THE PLANE FOR OVER 2 HRS; MAINT STATED THAT THEY COULD NOT FIND THE LEAK. IT WAS DECIDED TO SEND OUT THE FLT AND IF THERE WAS NO FURTHER PROBS AFTER ABOUT 60 MINS WE COULD CONTINUE TO ORD. IF THERE WAS A PROB WE COULD DIVERT TO LHR. TKOF AND CLBOUT WERE UNEVENTFUL. I WENT BACK FOR MY BREAK AND IN ABOUT 1 HR THE FO CAME BACK TO KEEP ME INFORMED. HE SAID THAT THE R SYS WAS DOWN TO THE REFILL MARK AND THE CTR WAS DOWN SLIGHTLY ALSO. HE TOLD ME THAT THE CAPT DID NOT WANT TO DIVERT TO LHR OR EVEN TO CALL LHR MAINT FOR ADVICE ON THE HYD SYS. WE CONTINUED ON BUT KEPT A CONSTANT WATCH ON THE HYD QUANTITIES. THE QUANTITIES ON THE CTR AND R SYS CONTINUED TO DECREASE AT A VERY SLOW RATE. ON COAST-IN THE CAPT AGAIN DECIDED NOT TO CONTACT DISPATCH EITHER BY HF OR COMMERCIAL RADIO. WE DID SEND SEVERAL ACARS MESSAGES ABOUT OUR HYD QUANTITY AND ASKING DISPATCH TO ADVISE ORD ATC THAT WE WANTED A LONG RWY FOR LNDG. WE DISCUSSED LNDG WITH THE R AND/OR C HYD SYS OUT. WE DISCUSSED TURNING OFF THE R HYD PUMPS TO SAVE FLUID BUT THE CAPT DECIDED TO LEAVE THINGS AS IS. AS WE DROPPED GEAR AND FLAPS THE QUANTITIES DECREASED FURTHER BUT THE LNDG WAS NORMAL. AFTER WE GOT TO THE GATE AND AFTER SHUTDOWN THE R SYS WENT TO ZERO. WE FOUND THAT A LARGE SPRAY OF HYD FLUID CAME FROM THE R WHEELWELL. SUPPLEMENTAL INFO FROM ACN 372107: FO SUGGESTED PROB WITH R SYS AND QUESTIONED THE CTR SYS WRITE UP IN LOGBOOK. FO SUGGESTED PRECAUTIONARY LNDG IN LONDON DUE TO THE POTENTIAL PROB INVOLVING CTR AND R SYS AND THE AVAILABILITY OF MAINT OR SPARE AIRPLANE. CAPT DECIDED TO CONTINUE TO ORD WITH ALTERNATES IN MIND. ON ARR PHASE COCKPIT CREW BRIEFED ABNORMAL APCH AND LNDG REQUESTING LONG RWY AND SPDS DUE TO POSSIBLE HYD FAILURE. NORMAL APCH/LNDG TOOK PLACE WITH NEAR TOTAL LOSS OF CTR AND R SYS FLUID ON GEAR EXTENSION. RESERVE BRAKES AND STEERING WAS USED ON SHORT FINAL.