A general rule of thumb to unfreeze a sewing machine is to find a spot where the mechanism moves and follow it to where it doesn't move. Then apply oil, maybe a little pressure, maybe some heat from a hair dryer. Eventually, you'll get everything moving again.
I'm in the "I use Tri-flow" camp. One person, somewhere, wrote that you shouldn't use it on sewing machines, versus all the people who use it and love it. Of course, your mileage may vary.
Tate