AN ACR WDB HAD TO DIVERT LAND AFTER AN IMPROPER MAINT PROC.

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THE ACFT ARRIVED IN SEOUL WITH A LOG WRITE-UP INDICATING THAT THE #3 L-HAND HYD PRESSURE LOW LIGHT ON; AND THAT SYS PRESSURE INDICATED NORMAL. SEOUL TROUBLESHOT THE #3 ENG L-HAND HYD PUMP PROB AND FOUND THAT THE INPUT SHAFT HAD BEEN SHEARED. ACR A MEL REQUIRES THAT AN INOP HYD PUMP MUST EITHER BE REPLACED; OR HAVE THE PUMP REMOVED AND A BLANKING PLATE INSTALLED. ACR A DID NOT STOCK A SVCABLE PUMP IN SEOUL; AND ALSO DID NOT HAVE A BLANKING KIT AVAILABLE. SEOUL PLACED A CALL TO ACR B; TO SEE IF THEY HAD A SVCABLE PUMP THAT ACR A COULD BORROW. THE ONLY HYD PUMP THAT ACR B STOCKS; IS A X PUMP; WHICH ACR A NO LONGER USES; BUT IS STILL AN ACCEPTABLE PUMP TO USE. I GAVE THE AUTH TO SEOUL TO USE THE X PUMP FROM ACR B AND TO CREATE A DEFERRED ITEM TO HAVE PUMP REPLACED AT THE EARLIEST MAINT OPPORTUNITY. ALSO AVAILABLE TO SEOUL WAS MAINT MANUAL REF THAT CONTAINS INFO REGARDING THE REMOVAL AND INSTALLATION OF AN X HYD PUMP. SEOUL COMPLETED THE REPLACEMENT OF THE HYD PUMP; LEAK CHKED THE PUMP INSTALLATION; AND MADE THE NECESSARY DEFERRED ITEMS TO HAVE THE PUMP REMOVED. FLT DEPARTED SEOUL. AFTER TKOF; RECEIVED ACARS MESSAGE FROM CREW THAT THEY WERE LOSING ENG OIL FROM THE #3 ENG. THE FLC PULLED AND RESET CIRCUIT BREAKER FOR #3 ENG OIL QUANTITY INDICATOR; WITH NO CHANGE IN THE CONDITION. I SENT THE CREW AN ACARS MESSAGE INDICATING THAT I BELIEVED THE INDICATOR WAS INDICATING CORRECTLY; AND WHAT THEY WERE PROBABLY LOSING ENG OIL FROM THE #3 ENG. I INSTRUCTED THE CREW TO FOLLOW THE PROCS IN THEIR FLT MANUAL; AND TO BE PREPARED TO SHUTDOWN THE #3 ENG IF THEY LOST OIL PRESSURE. SHORTLY AFTER THAT; RECEIVED MESSAGE FROM CREW THAT THE OIL QUANTITY WAS NOW READING ZERO; BUT PRESSURE WAS STILL GOOD. FLT LANDED IN NARITA; JAPAN; WITH THE #3 ENG STILL RUNNING. HOWEVER; THE #3 ENG OIL PRESSURE INDICATION BEGAN FLUCTUATING; AND THE CREW ELECTED TO SHUTDOWN THE ENG ON TAXI-IN. I HAD CONTACTED MAINT IN NARITA AND INFORMED THEM PRIOR TO LNDG THAT THE #3 ENG WAS LOSING OIL; AND THAT I BELIEVED THE PROB WAS WITH THE #3 L-HAND HYD PUMP THAT WAS JUST INSTALLED. AFTER THE ACFT HAD TAXIED IN; NARITA REMOVED THE PUMP AND FOUND THAT THE PUMP HAD BEEN INSTALLED WITHOUT THE DRIVE SPLINE O-RING INSTALLED. NARITA THEN INSTALLED THE BLANKING PLATE KIT PER THE MEL; AND RESVCED THE ENG OIL.