I got the printer out over the weekend! It still works, and I tried printing a couple of pages with the (empty) cartridge that was (fortunately) still in it.

It appears that this cartridge has been refilled once or twice before, but the most puzzling thing is that it's a Cannon BC-01 cartridge-why :?: ? But anyway, I refilled it with 2ml of ink from an "empty" modern cartridge , and it printed half a page, so is certainly working.

Now all I need is a jar of ink...