I just used John Deere corn head grease myself. I was going to use CV joint grease but the corn head grease will actually "flow" into the bearing cages and such in the box. I removed the lower side cover bolt for a vent and made a pipe plug fitting with a grease zerk in it to go in place of the fill plug. I filled the box until new grease ran out the lower hole where the bolt was removed. I reinstalled the bolt and put the factory fill plug back in place. It took me a full tube to fill it.