Remove the top valve cap from the casing by turning it counterclockwise. This will expose the inside rotor allowing you to apply oil directly to the top of the rotor.
Apply three to four drops of oil directly to the center of the rotor valve and move the trigger back and forth to ensure that the oil is evenly distributed throughout the rotor.
Replace the valve cap on top of the casing by turning it clockwise. Make sure the top lines up correctly so that you don't strip the valve casing threads.
Turn the French horn over and apply three to four drops of oil into the hole in the bottom of the rotor valve casing. Move the trigger to ensure that the oil is distributed.