The flat face of the C20 nut shown buts nicely up against the flat face of the C3 carrier. I use a small amount of grey Threebond on the inner face of the C20 nut, on final assembly do the nut up by hand, then tighten fully with a socket bar or rattle gun to a good 60 Ft/lB'S until one of the three slots in the mainshaft aligns with a slot in the C20 nut. Never had one leak, never used "O" rings or the modified Dowty seals in there unless it was set up that way to obtain the right distance for some end float, no less than 10 thou........Use a tiny amount of antiseize on the C5/1 clutch shoe drive pins as these can stick. And a very small wipe of oil in the bushes on the plate carrier, wipe away any excess or else it will end up on the shoe linings...........Don't make any of the parts/fits too tight as this will make the clutch stick in action............Good luck.