I dug through my tubing collection, found one that fit snugly in the filler hole, then one that fit over that tube, then another over the second one so I ended up with the third tubing large enough to jam a funnel into. I set the funnel between the seat and the metal seat surround, pour the correct amount of gear oil in the funnel, walk away for 15-30 minutes, time enough to empty the oil into the rear case.