EMB120 ACFT WAS LOW ON OIL AT START OF FLT; BUT REFILLED. THEN ENRTE OIL PRESSURE DROPPED AND FLC FOLLOWED PROPER HANDBOOK PROCS REDUCING THE PWR LEVER TO BELOW 75% NH. AT THAT PWR SETTING THEY WERE UNABLE TO MAINTAIN ALT AND ATC PROVIDED DSCNT CLRNC AS WELL AS DIRECT THEIR DEST.

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IN CVG OUR TRIP STARTED. UPON PREFLT OF AIRPLANE; #1 ENG HAD NO OIL IN SIGHT GLASS. CALLED MAINT; THEY ADDED 6 QUARTS OIL; DRY MOTORED THE PROP AND GOT THE OIL LEVEL UP. MAINT OK'D THE PLANE TO BE FLOWN. FLT FROM CVG TO BHM; OK. IN BHM; CHKED OIL LEVEL OK; NORMAL ENG START UP. FROM BHM TO MCO; IT WAS OVER TLH THAT WE LOST SOME OIL PRESSURE; IT DROPPED TO 50 PSID. WE PERFORMED THE CHKLIST WHICH REQUIRED BRINGING THE PWR BACK UNTIL ENG INDICATED 75% NH (HIGH PRESSURE SPOOL). #1 PWR LEVER WAS NOW AT FLT IDLE. WE WERE UNABLE TO HOLD ALT; SO WE ASKED ATC FOR A DSCNT. EXPLAINED THE SIT; ASKED FOR DIRECT ORLANDO BUT DID NOT DECLARE AN EMER. WE REDUCED THE ELECTRICAL LOAD ON THE GOOD ENG; STARTED THE APU TO RUN THE AIR- CONDITIONING. WE MADE ALL THE NECESSARY CALLS TO COMPANY AND MAINT. THEY OK'D THE CONTINUATION OF FLT TO MCO. IF PRESSURE DROPPED BELOW 45 PSID; WE PLANNED TO SHUT IT DOWN AND DIVERT TO GAINSVILLE. THIS DID NOT HAPPEN. SAFELY COMPLETED THE FLT TO MCO. MAINT MET US TO PICK UP THE PLANE AND TAKE IT TO THE HANGAR. THEY DISCOVERED THE OIL BREATHER WAS LEAKING OIL.