Japanese Eyedropper Servicing, An Introductory Exploration

[By "Introductory", I mean servicing eyedroppers is entirely new to me. I'm not an authority on these pens posting some sort of freshman 101 class]

It's been a while since I turned my attention to this project; my apologies to those interested. In the last post, the threaded boss was removed from the barrel of a Japanese eyedropper fountain pen, with the ultimate goal of changing the seals. This raised more questions, as the seals appear to be enclosed within the threaded boss rather than held inside the barrel by it.

At the time, I suspected the textured areas at either end of the boss to somehow provide access - here's a recap of progress so far, uploaded on the 5th. I had to put this project to one side shortly after, till today.

To bring things up to date, a good peer through a loupe and some decent sunlight revealed some extra machining on the blind cap side of the boss; I think the area highlighted is a separate piece, removable from the rest of the boss. It's very hard to make out, but I think a rubber O ring is visible below the recess too.

I reckon this bung provides access to the seals.

So, how to remove it? Some sort of expanding collet? Access would be better without the shut-off shaft in the way, and happily it does look like the shaft can be unscrewed from the blind cap. The awful photo below is the best of a very bad bunch; hopefully you can just about see the shaft threads, which are smeared with some sort of adhesive.

The blind cap assembly, I've sharpened this photo to help the threads
stand out. Sorry about the white balance
and glare.

I think an overnight soak in glycerine is in order; after that, we'll see about heating and waggling with section pliers to free the shaft from the blind cap.

To be continued...