I have been working on refurbishing an old machine that was totally frozen up with rust. Nothing at all moved even a little bit.
Dosed it liberally with sewing machine oil all over both in any space that it looked like oil could possibly drain into and all over the finish as well.
Cleaned off lots of rust with a soft cloth.
Soaked base overnight in a tupper with a bottle of transmission fluid per suggestion here on board. A few things started wiggling but still locked up.
Next step was PB Blaster sprayed only on the underside. Let set awhile and eventually with gentle rocking of the hand wheel it is now moving freely.
This is my first venture into refurbishing and I'm finding it fascinating and a combination of frustrating and rewarding!
Good luck on your adventure!