I have 2 Winfields, But no Crystal. Sounds like yours is Rust Welded at the threads.
Have you tried the electrolytic rust removal. "With such a nice Winfield, I would try on a Junker first".
"You will find a discussion of electrolytic rust removal back at the 6/29/07 posting by Willis Miller. Inside that string at 7/4/07 is a link to a video on the subject that's a good place to start. BB"
I haven't got mine built yet. Still gathering hardware.
Another link from George Klinzing. "I found a link at the Griswold and Wagner society with setups for this method of rust removal that should work for lanterns also. The link is" http://www.wag-society.org/Electrolysis/electros.php
Hope this helps!
And thanks to all for you help on my project.