After finding a few other people with the same problem, I read that someone had found that the adjustment needle had a "step" on it, to prevent it from being removed when under steam, the step pressing against the gland nut when the valve was fully opened. In some cases this "step" also blocks the small hole in the lubricator and very little steam is admitted. I learned that if one packed the gland nut with graphited yarn, this would stop the gland nut from screwing so far in, thus the step would clear the hole in the tube in the lubricator. I tried this, and discovered that testing it with the lubricator cap removed, a great deal more steam now issues from the hole in the top of the tube than before. However after running the loco on blocks for 45 minutes, there was no condensate in the lubricator. I will say that the loco has never shown any signs of running "dry", it has always run very smoothly, and there has always been a slight trace of oil on the piston rods, a small accumulation of oil under the cylinders and a few droplets of oil at the top of the chimney, so it must have been getting enough... but I would rather have a little too much than too little !
Puzzled by the fact that more then enough steam was being passed by the adjustment valve, I then took a look at the lubricator cap. A measurement taken from the flat bottom of the cap to the O ring showed that the cap was screwing in to a depth of 6.9mm, measuring from the top of the lubricator to the top of the pipe (and hole) in the lubricator, showed the same measurement of 6.9mm. So I guessed that the bottom of the cap was quite effectively blocking the hole. I fitted a thicker O ring, and hollowed out the bottom of the lubricator cap. A 45 minute test run this past weekend, resulted in a third of the lubricator filled with condensate and normal looking oil remaining !
So if you ever have an Accucraft loco with one of these new fangled adjustable lubricators, which uses very little oil, this may be of help.