A large portion of the machines I get are "frozen".
be very careful at this stage. Force is NOT what you want to be using. These machines were made with very tight tolerances so it is easy for two pieces to have moisture develop a rust bridge across parts. If you use force at this stage you will cause more wear and tear than decades of use....
I use the following stages:
1. Sewing machine oil. Every single location where unpainted metal moves against unpainted metal.
a. under the bed including every bit of the hook mechanism
b. remove face plate oil every nook and crannies
c. remove any rear access oil every thing that moves (baptize the bugger)
2. if an our or so of that does not do the trick, then i move on to Kriol (penetrating fluid, you can also use PB Blaster)
a. Same locations as before (BE VERY CAREFUL of decals with these.
I only have two machines that this did not work on, and both have two metal parts that are fused completely. I figure a few more weeks and patience and they will move too.
Most move in less than two hours.