Also may I say that you have a beautiful use of language and I wish you every success in your studies with your new pen.
I can't tell you how lovely this is to hear! It really brightened up a rainy day Also Coombe is not far from my family home at all, so thanks so much for that recommendation.
I'm very grateful for all this advice from everyone. What a lovely community! I managed to pop into town after uni, just before the shops closed, to get some ink. I flushed out the pen again and put through the Waterman ink. It showed slight promise (it kept flowing when the water had a tinge of ink to it, which I don't think happened before), but to no avail unfortunately. The flow stopped completely soon after the mark on paper was visibly pigmented. I've ordered some ammonia and Rapidoeze from Amazon, and I'll await those and see how they go.
When I was in the shop I also bought a Lamy 045, as I hadn't realised that they made slimmer pens and it really took me. It seemed like a good idea (perhaps for everything but my purse...) to get a reasonable pen that I like writing with whilst the whole saga plays out, especially after I've noticed my writing hand hurting at the end of long days of pressing hard to write with non-fountain pens. I'd still like to either replace or get working the really lovely pen, but it's nice to have something to write with. They only had the display one in stock, but she didn't think anyone else had tried it out, so I got it for £25 with some cartridges thrown in. It's nothing like the wonderful Yard-o-led, of course, but I am really impressed with it and I'm so happy that I picked it up! So nice to be back to using a FP.
The lady in the shop was very sweet and interested in the whole thing, as John Lewis (a major UK department shop, from where I actually purchased my pen originally) has just stopped selling Yard-o-led. She said that she particularly recommended Cross pens, and they tend to be slim. I don't think anyone's mentioned them here. Is there a reason? Anything I should be wary of?
Thanks again for so many helpful comments,