Craig, I use "O" rings there.......To fit a seal the outer end of the shaft needs to be machined to take a very small section seal.........Obviously the bronze bush would need to be slightly shortened to do this. You have to exercise a lot of care when passing the G 3 shaft through this seal as the spline for the kick start ratchet gear will damage the seal very easily, plus the circlip groove as well. A smear is a a light coating that covers the inner face of the C 20 nut, around the outer edge so that it forms a seal on the mating face of the C 3........Like I said, if the C 3 is a nice fit on the mainshaft, with no back and forth play, then this seams to work well..........If the bushes in the G 4 are good without excessive play, the gearbox should not leak badly from there.......The factory spec of oil quantity was 2 pints (1200 ml's) ......I generally put one litre in and add about another 100 ml's until the oil just shows on the tip of the dip stick........Using the full 1200 ml's can result in the box leaking........One litre is actually plenty enough anyway........I use 80 w 90 gear oil in all the gearboxes.