There is no separate gearbox. It's tucked inside the engine and utilizes the engine oil.
Use ONLY the specified oil in the final drive, going with a full synthetic such as Mobil 1 doesn't hurt. While alternatives MAY work, or have similar specs, many times they are detrimental to O-rings, seals etc. on an application it isn't made for, and may not protect bronze, brass and ??? whatever else may be hiding in there somewhere.
Use ONLY the specified oil in the final drive, going with a full synthetic such as Mobil 1 doesn't hurt. While alternatives MAY work, or have similar specs, many times they are detrimental to O-rings, seals etc. on an application it isn't made for, and may not protect bronze, brass and ??? whatever else may be hiding in there somewhere.