Leakless primary chaincase

Your back wheel is going round at about 1000rpm max, your crank is going round at 7000rpm, you would need some seriously sticky, anti fling chain lube to stay put it there. But then most single cylinder racing Nortons only give the primary chains a squirt of oil now and then. Once that snot has sprayed all round the inside of the chaincase it would probably be oiltight.

The chain in the chaincase gets quite hot, as do all components in there, so chain lube will be thrown off in no time and your chain won't survive it. I once tried it on an AJS single- you could stand the chain in a corner after 200 miles and use it as a walking stick!

I use a new o-ring between the chaincase halves every time it have it apart (which is probably once in 2-3 years, if that), and replace the felt seal behind the clutch every time I have the chaincase off. I don't see the Commando chaincase as problematic regarding oiltightness.

I use ATF oil which is quite thin so if that isn't a problem, what is?

The pressed steel sliding plate in the back of the primary chaincase , ideally needs to be centralised on the gearbox shaft to maximise the effect of the felt oil seal. Moving the gearbox to adjust the primary chain may not move the steel plate with it, leaving a gap to one side of the felt. Food for thought on this. Fit the primary drive fully and adjust the Primary chain. Then remove the primary drive and centralise the steel felt holder by tapping into position with a suitable tool. Re-fit the primary drive. All a bit tedious but if a job's worth doing etc.