What was found
WITH LEFT FMC DEFERRED (REF 34-63/6185) RIGHT AUTOPILOT FAILED IN CRUISE AT FL390 AND WOULD NOT RE- ENGAGE. ALSO VNAV INOP AT THAT POINT. ENROUTE TO MIA CREW ADVISED ALL 3 AUTO PILOTS ARE INOP. DURING LANDING IN MIA CREW EXECUTED A MISSED APPROACH. ON GO AROUND A EMERGENCY WAS DECLARED. AIRCRAFT LANDED SAFELY. CRASH, FIRE AND RECUE RESPONDED WITH NO ACTION REQUIRED. REPLACED L FMC AND LOADED SOFTWARE FACTED MEL (REF 34-63/6185) AND PLACED R A/P ON MEL.