Unfortunately, the brass ferrules and iron damper rod create the electrolysis effect and weld together. I doubt you'll ever get them freed up. I had a kit that Willys sold in order to repair it. Getting the old one out was an awful ordeal. I had to drill, heat and pound to get the old one out.
The best thing to do is if it is stuck open (the damper in the horizonal position) just leave it. If it's in vertical postion or close to it, use a hack saw or a torch and remove it and operate without it. Mine's been stuck open for 30 years and the car runs fine. Unless you drive on cold days, it really won't matter.