B737-400 ACFT. RPTR CAPT WAS INFORMED OF A HYD LEAK DURING HIS WALK AROUND INSPECTION. MAINT ASSURED THE CAPT THAT IT WOULD BE REPAIRED PRIOR TO DEP. ANOTHER FUEL GAUGE PROB DEVELOPED AND MAINT HAD TO MEL THAT ITEM. HOWEVER; MAINT FAILED TO WRITE UP OR SIGN OFF THE HYD PROB AND IT WASN'T DISCOVERED UNTIL AFTER THE NEXT FLT LEG.

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DURING WALKAROUND; MAINT BROUGHT A HYD LEAK TO ATTN OF CAPT (ME). I CHKED IT OUT AND WAS ASSURED IT WOULD BE FIXED. I WENT ABOUT MY OTHER DUTIES AND INSURED THAT MAINT HAD THE MAINT LOG SO THEY COULD WRITE UP PROB THEY FOUND. A FEW MINS LATER; FUELER HAD A PROB WITH FUEL GAUGES IN WING FUELING PANEL. MAINT LOOKED AT IT AND DETERMINED THAT THIS PROB WOULD REQUIRE AN MEL. JUST BEFORE PUSH; MAINT CAME TO COCKPIT; CHKED HYD QUANTITY INDICATORS -- THEY HAD GONE FROM 85% TO 100%. HE INDICATED TO ME THAT HE HAD FIXED PROB. WE THEN DISCUSSED THE MEL AND CHKED MAINT LOG FOR MEL. I MISSED THE FACT THAT MAINT HAD NOT WRITTEN UP OR SIGNED OFF HYD LEAK DISCREPANCY. AFTER 1 LEG TO ANC; DURING WALKAROUND; THE FO NOTED THE HYD LEAK AGAIN. WHEN I WENT TO THE LOG TO WRITE IT UP AS A REPEAT; I DISCOVERED THAT IT HAD FAILED TO BE PLACED IN THE LOG IN FAI. INSTEAD OF HIDING THIS; I CHOSE TO INFORM MAINT THAT THIS WAS A REPEAT WRITE-UP BY STATING THIS IN THE LOG. SINCE I WROTE IT UP THIS WAY; IT ALSO SHOWS MY FAILURE TO INSURE THE LOG WAS CORRECT IN FAI. I FELT IT MORE IMPORTANT TO INSURE THE LOG WAS CORRECT AND ELECTED TO PLACE MY ERROR UP FRONT. THE PROB WAS FIXED AGAIN IN ANC. MORAL: YOU GOT TO CHK THE LOG! IF YOU KNOW ABOUT A PROB; PUT IT IN THE LOG YOURSELF.