COMMUTER SMT FLC FAILS TO GET REPAIRS ON MODE C PRIOR TO DEPARTING ON THIRD LEG OF TRIP.

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WE WERE OPERATING AN SMT FOR ACR ENRTE FROM HNL TO LANAI- KAHULUI (MAUI)-HANA-KAHULUI-MOLOKAI-HNL. DEPARTING HNL'S CLASS B AIRSPACE WE WERE ADVISED THAT OUR MODE C WAS INTERMITTENT AND HANDED OFF TO HONOLULU CTR. THE WX IN THE LANAI AREA WAS IFR CAUSING US TO MISS APCH ON THE VOR RWY 3 APCH. THIS LEG WE WERE ON AN IFR FLT PLAN. LANAI IS AN UNCTLED FIELD; SO WE CONTACTED OUR PREVIOUS CTR CTLR AND REQUESTED IFR ROUTING TO KAHULUI. AT SOME POINT IN TIME; WE WERE AGAIN ADVISED OF OUR MALFUNCTIONING MODE C; AND TOLD TO RPT REACHING CERTAIN ALTS. APCHING KAHULUI WE WERE HANDED OFF TO MAUI APCH. MAUI WAS MARGINAL VFR; SO WE WERE PRETTY BUSY AGAIN PREPARING FOR AN INST ARR. I'M NOT SURE IF WE WERE QUESTIONED BY MAUI APCH ABOUT OUR MODE C. IN OUR QUICK TURNAROUND IN KAHULUI I WAS BUSY WITH CALCULATING OUR REFUELING AMOUNT; WT AND BAL; AND; MOST IMPORTANTLY; THE WX FOR OUR 30 NM TRIP TO HANA (HANA ON THE NE CORNER OF MAUI HAS NO INST APCH). WE DEPARTED KAHULUI AT APPROX XX30 BOUND FOR HANA AND WHEN TWR HELD ON TO US FOR LONGER THAN NORMAL WE THEN REMEMBERED THE PROB WITH OUR MODE C. TWR SWITCHED US TO THE SAME CTLR WHO WAS WORKING US IN ON APCH. HE ADVISED US OF NOT RECEIVING OUR MODE C AT WHICH TIME WE REQUESTED AN FAR DEV TO FLY TO HANA AND RETURN TO KAHULUI. OUR REQUEST WAS APPROVED ON THE CONDITION THAT WE HAVE IT REPAIRED IN KAHULUI BEFORE WE DEPARTED TO MOLOKAI. IN HANA I CALLED HNL MAINT AND WAS ABLE TO DEFER THE MODE C ACCORDING TO OUR MEL. THE STIPULATION IN THE MEL ALLOWED US TO OPERATE IN THIS CONDITION AS LONG AS WE GET AN ATC AUTH DEV PER FAR 91.215. WE ALSO CALLED OUR COMPANY AND THEY WORKED OUT THE DEV WITH ATC. FROM THAT POINT ON WE WERE TECHNICALLY LEGAL TO OPERATE WITHOUT THE MODE C; BUT THE PROB SHOULD HAVE BEEN TAKEN CARE OF IN KAHULUI BEFORE OUR HANA FLT. HOPEFULLY; THE NEXT TIME BEFORE THE WX OR ANY OTHER FACTORS OVERLOAD ME; I'LL SLOW DOWN AND MAKE SURE ALL BUSINESS IS TAKEN CARE OF BEFORE DEPARTING.