Re: 1967 Mercury 110 9.8hp Lower Unit
You don't need to do anything with the screw that says "flush". It has nothing to do with the lower unit oil. All you need to do is remove the "middle screw" which is the vent. Then fill through the bottom screw hole until it flows out the vent hole. Replace both screws. Also it is wise to replace the gaskets for both screws. Very little oil is needed for the lower unit.