A B737-800 WAS DISPATCHED WITH THE LEADING FLAP GREEN EXTEND INDICATION LIGHT DEFERRED. NOT ILLUMINATED WITH THE FLAPS AND SLATS EXTENDED.

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RETURNED TO THE GATE FOR MAINT FOLLOWING AN UNSUCCESSFUL ATTEMPT TO LOWER FLAPS FOR TKOF. DURING TKOF CHKLIST; FO NOTICED THE AMBER LEADING EDGE FLAPS TRANSIT LIGHT ILLUMINATED WITH THE FLAPS SET FOR TKOF. THE GREEN LEADING EDGE FLAP LIGHT FAILED TO ILLUMINATE EVEN THOUGH THE FORWARD FLAP AND THE OVERHEAD ANNUNCIATOR PANEL FOR THE LEADING EDGE FLAP DEVICES INDICATED FLAPS/SLATS IN PROPER POS FOR SELECTED POS. THE ACFT HAD THE SAME WRITE-UP 2 DAYS EARLIER AND MAINT SIGNED THE GRIPE OFF AFTER REPLACING THE FSEU CTL COMPUTER THAT APPEARED TO FIX THE PROB. AT THE GATE WITH THE FLAPS SET FOR TKOF; THE FO AND CONTRACT MAINT CONFIRMED THAT THE FLAPS/SLATS WERE SYMMETRIC AND IN THE POS SELECTED. AFTER TROUBLESHOOTING THE PROB AND IN A 3-WAY CONVERSATION WITH DISPATCH; MAINT CTL AND LCL CONTRACT MAINT PERSONNEL; THE DECISION TO PLACARD THE LEADING EDGE FLAP TRANSIT LIGHT INOP WAS MADE AND DEFERRED PER MEL 27-1A. AFTER COMPLYING WITH THE PROVISOS OF THE MEL; WE LAUNCHED FOR THE SECOND TIME. WHEN PWR WAS ADVANCED FOR TKOF; THE TKOF CONFIGN HORN SOUNDED AND I IMMEDIATELY PULLED THE PWR TO IDLE TO DOUBLECHK OUR CONFIGN. HAVING CONFERRED WITH THE FO AND CONFIRMING THAT THE PROPER CONFIGN WAS ESTABLISHED EXCEPT FOR THE GREEN LEADING EDGE FLAP EXTENSION NOT ILLUMINATED BECAUSE OF OUR PLACARDED ITEM; I ELECTED TO TAKE OFF KNOWING THAT THE HORN WOULD SILENCE ONCE WE WERE AIRBORNE. ENRTE AFTER MORE CAREFUL DELIBERATION WITH MY FO AND THE MEL; I FELT THAT THE MEL WAS AMBIGUOUS FOR THE SITUATION AT HAND AND THAT WE MARCHED DOWN THE WRONG DECISION MATRIX TREE IN SOLVING THE PROB BECAUSE THE REAL ISSUE MIGHT BE A COMPUTER OR SENSOR ISSUE NOT COVERED BY THE MEL. I SENT AN ACARS MESSAGE TO DISPATCH REQUESTING MAINT PULL THE ACFT OTS UNTIL THEY COULD DETERMINE THE ROOT CAUSE OF THE IMPROPER LIGHTS. AS LUCK WOULD HAVE IT; THE FLT WAS UNEVENTFUL WITH THE FLAPS/SLATS WORKING PERFECTLY ON LNDG. FURTHERMORE; IN AN ATTEMPT TO HELP MAINT TROUBLESHOOT THE ISSUE; THE PROB COULD NOT BE DUPLICATED ON THE GND WHILE TAXIING IN WITH THE LIGHTS WORKING AS ADVERTISED. IN RETROSPECT; I FELT WE CONDUCTED THE FLT SAFELY; HOWEVER; WE INDIRECTLY MAY HAVE FOLLOWED THE WRONG PATH IN RECTIFYING THE SITUATION. INDIRECTLY; I WAS TRYING TO GET OUR PAX SAFELY TO THEIR DEST WHILE ATTEMPTING TO GET THE ACFT IN A BETTER LOCATION TO FIX THE PROB CORRECTLY.