If it is necessary to add lubricant, use SAE 90 Gear Oil. In extremely cold weather use SAE 80 Gear Oil or dilute SAE 90 Gear oil with a small amount of SAE 10W engine oil to decrease steering effort. Install the filler plug.
This check is only required on models through 1973; later models are permanently lubricated.
Clean the area around the filler plug, and remove the plug. The level of lubricant should just cover the worm gear.