Thanks for the very detailed response. I really appreciate it. Last night I took apart the transformer, trying to find the hair width copper strand which connected 20/21. It’s MIA and if it was there, I can’t find it anymore to resolder.Suggest one more quick measure of the transformer AC voltage across 30-31. Keep an eye that the meter is on the "AC" range and an eye for V vs. mV on the readout as suggested above. I've more than once tried to measure AC while on the DC range by accident and it reads about 0V. For your question above, measuring the voltage in various ways will in no way harm the transformer.
The low input voltage of about 210 VAC instead of 230 VAC would lead to about 22-23 VAC on the output of the transformer like you reported prior when you were measuring from ground. If the transformer is NOT grounded that can just be a ghost reading. However, did you confirm if the transformer is tied to ground? To do that, unplug the mill from the wall and measure for continuity between 30 and ground and 31 and ground. Do all of the green terminals you metered to also tie to ground?
It very well could be a bad transformer but worth a quick re-check I think.
The gentleman I purchased the mill from actually works for the company where that transformer posted above is located. So he is getting me his price and should have it fairly soon.
I wasn’t able to test for ground as your described, I just looked for some sort of ground wire and assumed that was a no. I suppose a mute point now.