How do you check the gear oil in the lower end of a 1984 mariner 115 hp?

To check the gear oil in the lower end of a 1984 Mariner 115 hp outboard motor, first ensure the boat is on a level surface. Remove the lower drain plug located on the lower unit and check for any oil leakage or water contamination. Next, replace the drain plug and remove the upper vent plug; oil should flow out if the level is adequate. If not, add the appropriate gear oil until it starts to seep from the vent hole, then reinstall both plugs securely.