B737-200 FLC MISREADS MEL REQUIREMENTS ON OXYGEN SYS AND OPERATES WITHOUT MAINT CHKING SYS.

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MEL VIOLATION. B737-200 HAD CREW DEFERRED MEL 35-3. PAX OXYGEN GAUGE INOP. I PICKED IT UP IN ZZZ WITH MEL ON DISPATCH FORM AND COLOR 1 TAGS POSTED ON INST AND IN LOGBOOK. FO HAD BEEN WITH ACFT FOR 3 LEGS. PAX OXYGEN GAUGE INDICATED NORMAL QUANTITY; ORIGINAL WRITE-UP WAS FOR ZERO QUANTITY INDICATION. MEL SAID CHK QUANTITY FOR PROPER DISPATCH AMOUNT. I ACCEPTED ACFT AND FLEW TO YYY. MAINT MET ACFT IN YYY AND CHANGED COLOR 1 MEL TAGS TO COLOR 2 MEL TAGS. INFORMED ME THAT PAX OXYGEN QUANTITY HAD TO BE CHKED AND DOCUMENTED BY MAINT PRIOR TO EVERY FLT INCLUDING CONTRACT MAINT AT OUT STATIONS. WE COMPLIED UNTIL ARRIVING IN XXX; WHERE ACFT WAS REMOVED FROM SVC. I FAILED TO COMPLY WITH THE MEL WORDING; WHICH SAID THAT CHKING PAX OXYGEN QUANTITY WAS MAINT PROC; NOT A PLT PROC. I WAS LULLED INTO A FALSE SENSE OF SECURITY; BECAUSE ACFT HAD JUST ARRIVED AT AN OUT STATION FROM A MAINT BASE. NEITHER SURRENDERING CAPT NOR CONTINUING FO MENTIONED ANY SPECIAL PROC OR PROB; AND PAX OXYGEN; BECAUSE GAUGE WAS INDICATING NORMAL; NOT ZERO QUANTITY. I SHOULD HAVE QUESTIONED THE COLOR 1 MEL TAG ARRIVING FROM YYY; I SHOULD HAVE QUESTIONED THE WORDING OF THE MEL; WHICH DOES NOT SPECIFY 'PRIOR TO EVERY FLT' NOR 'BY QUALIFIED MAINT PERSONNEL' (THAT IS SPECIFIED IN A NOTE 2 PARAGRAPHS BELOW THE MEL REQUIREMENT.) CAUSE OF INCIDENT -- COMPLACENCY. 1) NORMAL OPS VMC DAY. 2) JET APPEARS NORMAL INCLUDING PAX OXYGEN QUANTITY. 3) NO SPECIAL WORDS FROM OFF GOING CAPT OR CONTINUING FO. 4) VAGUE WORDING OF MEL. WARNING FLAGS I IGNORED: 1) COLOR 1 MEL TAG ARRIVING FROM MAINT BASE. 2) VAGUE WORDING OF MEL. SUGGESTED CORRECTIVE ACTION: 1) CHANGE WORDING IN BODY OF MEL 35-3 TO INCLUDE THE WORDS 'PRIOR TO EVERY FLT.' NOTE: THE 'M' DOES INDICATE A MAINT PROC. I SHOULD HAVE CAUGHT THAT. 2) RE-EMPHASIZE TO CAPTS THAT COLOR 1 MEL TAGS THAT ARRIVE IN A MAINT BASE MUST BE CHANGED TO COLOR 2 PRIOR TO DEP. 3) RE-EMPHASIZE TO MAINT THAT WHEN AN ACFT ARRIVES WITH A COLOR 1 MEL TAG; IT MUST BE CHANGED TO COLOR 2 PRIOR TO DEP. YYY GOT IT RIGHT; XXX GOT IT WRONG.