A B777 IN CRUISE AT FL370 DECLARED AN EMER; SHUT DOWN #2 ENG; AND DIVERTED DUE TO A VISIBLE R WING FUEL LEAK. CAUSE OF LEAK UNKNOWN.

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WE WERE IN CRUISE AT FL370 WITH A TANK TO ENG FUEL CONFIGN. AFTER PASSING YQB THE MESSAGE FUEL IMBAL DISPLAYED ON EICAS. WE DISPLAYED THE FUEL SYNOPTIC WHICH SHOWED THE R MAIN TANK APPROX 3600 LBS LESS THAN THE L MAIN TANK. WE STARTED THE FUEL IMBAL CHKLIST AND WERE FEEDING BOTH ENGS FROM THE L TANK. SHORTLY THEREAFTER THE CAPT RECEIVED A CALL FROM A FLT ATTENDANT. HE INFORMED ME THAT SHE RPTED THE R WING APPEARED VERY WET ON THE UPPER SURFACE. I CHKED THE PROGRESS PAGE 2; WHICH SHOWED THE TOTALIZER FUEL OF 98.7 AND CALCULATED FUEL OF 102.4. AT THAT POINT WE STOPPED THE XFEED WITH APPROX 1700 LBS LESS IN THE R TANK. THE CAPT HAD THE FO TAKE A LOOK AT THE WINGS. HE RPTED THE WING WAS INDEED VERY WET AND THE STREAMS OF LIQUID WERE CLR. HE ALSO RPTED THE L WING APPEARED DRY. THE CAPT THEN SENT ME BACK TO TAKE A LOOK. I OBSERVED THE R WING FROM 4 DIFFERENT WINDOWS AND SAW SEVERAL RIVULETS OF CLR FLUID RUNNING FROM FRONT TO BACK ON THE WING. THERE ALSO WERE ADDITIONAL FLOWS RUNNING ALONG SEVERAL SEAMS INBOARD TO OUTBOARD. THERE WERE LARGE AREAS OF THE WING THAT WERE WET INCLUDING THE INBOARD AILERON WHICH WAS SOAKED. THERE WAS NO CHANGE OR LESSENING OF THE FLOWING RIVULETS. THE ONLY COLORED FLUID I COULD FIND WERE 2 SMALL TRAPPED PUDDLES OF ORANGE FLUID ABOUT 2 INCHES WIDE LOCATED AT THE LEADING EDGE OF THE INBOARD FLAP. ALL THE OTHER FLUID WAS CLR. AT THIS TIME GANDER HAD US DSND TO FL330. WE NOTED THE R MAIN FUEL TANK GAINED ABOUT 2000 LBS DURING THE DSCNT. I DISPLAYED THE FUEL MAINT PAGE AND SAW NO DISCREPANCIES IN THE FUEL READINGS. THE CAPT CALLED DISPATCH WITH A PHONE PATCH TO MAINT. AFTER RELAYING THE INFO; THE DECISION WAS MADE TO DIVERT TO JFK. THE CAPT HAD ME INFORM MONCTON CTR OF OUR DIVERSION TO JFK AND DECLARE AN EMER. WHILE RUNNING THE FUEL LEAK CHKLIST THERE WAS SOME DISCUSSION ABOUT SHUTTING DOWN THE R ENG. IT WAS DECIDED TO SHUT IT DOWN SINCE BOTH THE CHKLIST AND MAINT RECOMMENDED TO DO SO. AFTER APPROX 20 MINS THE FO DID ANOTHER OBSERVATION OF THE WINGS AND RPTED THE R WING WAS COMPLETELY DRY. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED HE WAS THE RELIEF PLT AND WENT BACK TO OBSERVE THE R WING AND NOTED THE OBVIOUS FUEL LEAK. THE RPTR SAID IT WAS NOT A LARGE LEAK. THE RPTR SAID THE CORRECTIVE ACTION IS NOT KNOWN AS MAINT HAS NOT RPTED THE FIX OR THE COMPONENT REPLACED.