Re: johnson lower unit
Use what is called "Premium BLend" lube, also known as "Type C", available at your dealership.
Find a large slotted screw in the skeg of the lower unit about 7/16" in diameter..... this would be the drain screw.
Further up the gearcase, you will find a identical screw..... this is the opil level screw.
Remove both screws to drain the unit. Fill the unit from the bottom up. When the oil starts to flow out of the oil level hole, insert the screw into that oil level hole to create a air pocket so that you can then rmove the fill tube or hose from the fill/drain hole to insert the fill/drain screw.