Pilot capless 1960s not holding out

[jem14f]

Well it is kinda holding out on me..

I purchased an early Pilot capless (as far as I can tell it is a 1965 capless) as a parts pen and am trying to re-construct it, I basically had the shell.

I managed to track down the nib section and a bulb type converter, which now I have worked out how it fits, sits in the pen
and when I push the rear section cap down, pushes the nib out through the flap door.

The nib assembly pushes against a spring inside the front of the pen body and retracts via that spring, but does not hold in the
depressed position so that the nib would be exposed.

So I am missing part of the mechanism somewhere.

The only youtube I could find was in russian, but did show, what looks like a plastic collar around the ink view area (it could just be a protection part)

But I have no idea how the "click" hold works on these pens, I am assuming it has a clutch of some sort in the front part of the pen and that the rear section is basically a cover (this differs from the 1964 pens I have seen and the later pens where the click hold/release clutch is in a knob at the end similar to a ballpoint)

Does anyone have any experience with these or a diagram of how the earlier pens worked.

I must admit compared to the later pens this one seems flimsy, so may be a 1970s cheaper version but the only reference I have seen was indicated as 1965. Please see pictures attached with two internal shots of the front body where the nib assembly fits, I have placed an arrow to show the orientation slot and this turns into a bayonet fitting to hold the nib assembly inplace, in the second internal picture the spring below can be seen.

in hopes
Jeremy