Here is a link to an old post you might enjoy:
http://www.quiltingboard.com/vintage...r-t169127.html
Some times Tri-Flo will loosen up the stuck parts. Some times it is rust and you will have to use a bike chain oil - that oil is green and has detergents in it but it will loosen up rusted parts. Some times it is hard to tell the difference between rust and dried oil. Rust will be somewhat rough like sand paper. Oil will be somewhat gummy - rust is never gummy. I had a pressure foot stuck the other week on a Singer 201. I put T-F on it and nothing happened so I kept putting it on every couple days. I turned the machine upside down and put some on and let it set a while. Then one day Lovie and Wilbur were over so I said we would learn how to unstick a pressure foot. We oiled it a good one and then I loosened the spring and pulled on it a little tiny bit and it went. Then I readjusted the pressure (scary what Wilbur knows how to do...) Good as gold. Some times the oils used back in the day set up like superglue in the tubes the needle bar or the pressure bar go through and you have to heat them in order to get them to budge.