I did it! I used a thin screwdriver and gently tapped it at the division of the head and plate. I got enough space to spray it with penetrating oil. (I'm using Deep Creep on this and it seems to work well.). Waited a bit and tapped around it with a screwdriver. If anyone else tries this, be very gentle. I started tapping between the two slider plates and it started moving! Most of the rust was at the outside edge.
Its going to take work, but I'm getting closer. Thanks for the help!