A B737-300 WAS DISPATCHED WITH A THRUST REVERSER INOP IN CONFLICT WITH THE MEL. IMPROPER PROC USED TO RENDER REVERSER INOP.

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RECEIVED CALL FROM MAINT THAT ACFT HAD A LEAKING THRUST REVERSER DEPLOY LINE OUT AT THE REVERSER AND WORK WAS IN PROGRESS OF CHANGING THE LINE ASSEMBLY. RECEIVED SECOND CALL APPROX 20 MINS LATER THAT THE LINE COULD NOT BE REMOVED DUE TO LACK OF PROPER TOOLING. I THEN CHKED THE ACFT ROUTING FOR THE EVENING AND NOTICED IT WAS SCHEDULED TO REMAIN OVERNIGHT. I DISCUSSED WITH THE MECH THE OPTION OF CAPPING THE LEAKING LINE AND THEN LOCKING OUT THE THRUST REVERSER AND DEFERRING AND THEN HAVING THE LINE CHANGED OUT WHEN THE ACFT TERMINATED. I KNOW I HAD USED THIS PROB IN THE PAST ON -200 SERIES ACFT AND THOUGHT THE SAME PROC COULD BE APPLIED TO THE -300. ULTIMATELY; THE THRUST REVERSER WAS LOCKED OUT AND DEFERRED AND THE ACFT PLACED BACK IN SVC. SEVERAL HRS LATER; I LEARNED THROUGH DISCUSSION WITH OTHERS IN MAINT CTL THAT THIS PROC COULD NOT BE USED ON THE -300 ACFT AND NOTIFIED THE MAINT CTL TEAM LEAD. HE CONCURRED THAT THIS WAS INCORRECT APPLICATION OF THE MEL. DISPATCH WAS NOTIFIED IMMEDIATELY AND THE ACFT WAS TERMINATED FOR REPLACEMENT OF THE LINE ASSEMBLY.