Hi
Many thanks for all the responses, all most appreciated.
The photos from Izzy are good, but I've got all of this apart already without problems. It's getting the last piece out, shown still fixed to the body to the right hand side in Izzy's last pic. I think this is described as the spring guide in the very useful manual (thanks Mick). I've seen a strip down on YouTube so know it comes out, but it just will not turn. The photo attached shows it too. I have removed the needle via the chucking nut as per Guy, in a similar manner to other airbrushes I have used in the past.
I have only used cellulose thinners to spray through to clean after painting, or to wipe clean dismantled items, so hopefully I've not damaged any seals. From the exploded diagram it seems there is an O-ring in the spring guide, so clearly not ideal to use cellulose there. I don't have access to IPA being based in rural France, but do have surgical spirit and white spirit as well as the aforementioned cellulose thinners. The idea of leaving it in hot water is something I can try....but looking at the colour (which is a faint maroon which may not be visible in the pic) It may be an earlier use of enamel that is left as residue. If it is then that will be interesting. I don't have an ultrasonic bath, and am not convinced I need one. Well, I've never needed one before........