W&G Needle nut.
Janey gave me a call concerning your problem. From the picture you posted I don't think the nut that is there is really a W&G needle bar nut. I can't imaging a real W&G nut getting that bad. The problem is that the original nut was actually tapered and it probably is impossible to replace. It is not a common nut and I doubt that your granny really had any spares that would have fit. That is probably why things look a bit strange down there because someone tried to come up with a fix for a lost nut. I will try and look at some of my W&G machines and see if I can make a suggestion. In the mean time I would suggest that you try soaking the nut that is there with kerosene and let it set a couple of days to try and make the nut(?) that is there a little easier to remove. Will try and send you another post in a day or two.