Since gear oil is being talked about, OMC must be done differently than all others! They get drained the same way at the bottom, but must be filled using the fill plug located by the Cavitation plate. If you mistakenly fill from the bottom it will air lock but show a full reading, when you run it the air lock breaks the oil level drops and the upper will burn the gear set. And like the other post Merc HP oil is the way to go, deeper pockets can refill with Red Line.

MOP