KH125 oil leak on output shaft

[AMCQ46]

Hi All,
As the title says, my 1977 KH125A1 has a small oil leak on the gearbox sprocket shaft following the full bottom end rebuild. It only happens on the side stand when the bike is tipped over far enough for the oil level to be above the shaft, but it is making a mess on the garage floor, so I better get it sorted.

This shaft is a splined shaft, and when I stripped it down there was no obvious seal in there, but there is a sleeve that sits between the sprocket and the bearing [or it may go under the bearing, I cant remember now as it was 1 year ago when I did the rebuild].
In the gasket kit I got, there was an o-ring, but as there wasnt one when I took it apart, and I couldnt see how the o-ring would seal the splined shaft, I didnt fit it.

Question.
Has anyone got a x-section view of the output shaft assembled into the bearings and I can see if there should be a seal?

or

Has anyone got a similar vintage bike and knows what should be in there?

Thanks in advance

AMQ