Tom, I did try soaking with PB Blaster and Acetone/trans fluid, over about a year!
I finally used a propane torch to do heat/cool/penetrant/wax cycles and slowly got the shaft to start moving after about an hour!
I have at least 2 carbs that could use new shafts, primary and secondary.
I've seen replacement shafts for some Chev and Mopar applications, trying to find something that will fit, or find the manufacturer.
I haven't yet checked whether 1x4 carb parts will fit, thought I'd ask here first.
It's not a high priority right now, just trying to make progress on unfinished projects.