Sheila, thanks for you comments. I will probably have to replace the thumbscrew one day but am trying to postpone the day.
I found that Seyco has a replacement anvil for the thumbscrew so I screwed up my courage, got out the needle nose pliers, and with a gentle pull of the anvil separated from the body of the thumbscrew.
It seems to be held in by the friction of a tiny O-ring on the shaft of the anvil.
I'm going to try cleaning it with a damp cloth and see how it goes. I will put spare replacement chucks, thumbscrews, and set screws on my to-do list but now can continue with my Christmas scrolling.
Thanks,
Jim