WDB DEPARTS WITH DEFERRED MAINT ON FAULTY VHF EQUIP. NOT LEGAL ACCORDING TO MEL.

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FLEW FROM BUENOS ARIES TO SANTIAGO WITH 1 DUAL HEAD VHF COM RADIO. THE INBOUND RPTED DISCREPANCIES INCLUDED: #4 ENG DRIVEN HYD PUMP INOP;SHEARED DRIVE SHAFT REPLACED; #3 VHF COM INOP. DEFERRED. THE MAINT RELEASE MESSAGE STATED: #3 VHF COM TX AND RECEIVER WEAK; INTERMITTENT; OR INOP ON ALL FREQ. SHOULD READ #2 INOP ONLY. APPROPRIATE DEFERRED ITEM STICKERS WERE INSTALLED BY THE MECH AT DEP TIME. MY FO CHKED THE MEL DOCUMENT ON BOARD AGAIN AND READ THAT 1 RADIO INOP WAS OK. LATER; WE ALL READ THE MEL AGAIN AND REALIZED ONLY 3 VHF INSTALLATIONS CAN HAVE #2 VHF COM INOP FOR DISPATCH. THE NEXT LINE IN THE MEL; WHEN STUDIED; SPECIFIED 2 VHF COM RADIOS REQUIRED IN 2 VHF INSTALLATIONS; LIKE OURS. THE RETURN FLT WAS DELAYED 5 HRS FOR REPLACEMENT OF THE #2 VHF COM RADIO; WHICH CAME; WITH A MECH; OFF LINE. THE HUMAN FACTORS INVOLVED INCLUDED ACCEPTANCE OF 'OTHERS' JUDGEMENTS. IF IT'S DEFERRED; IT MUST BE OK. WE STILL HAD 2 HIGH FREQ RADIOS. THE ORIGINAL 'MRM' CODE SPECIFIED #3 RADIO; IN ERROR. 3 CREW MEMBERS QUESTIONED '1' RADIO OP; BUT DID NOT PIN IT DOWN. THE FLAGS WERE THERE WAVING IN THE BREEZE. THIS INCIDENT SHOULD NOT HAVE HAPPENED. SUPPLEMENTAL INFO FROM ACN 203241: CONTRIBUTING FACTORS -- THE PREVIOUS FLT FROM MIA-EZE HAD AN INOP CARGO COMPARTMENT FIRE WARNING TEST AND IT WAS LEGALLY DEFERRED. THIS HAD SURPRISED ME AT THE TIME; SO I WAS PREPARED TO BE SURPRISED AGAIN; ALTHOUGH IF I HAD TAKEN THE TIME TO THINK; I WOULD HAVE KNOWN MAINT WAS INCORRECT ON THIS OCCASION.