From what has been said and efforts applied I would guess that some well-meaning "craftsman" used Locktite or a similar product on the center shaft and minute tube to lock them tight. That would explain a lot and is also why the various solvents have had no effect. I would try the application of heat to the minute tube, Locktite green releases at about 500 degrees F IIRC. So, it needs to be hot, just not too hot. And of course, don't apply the torch/heat anyplace close to your various solvents. Many of them burn explosively just in case we need to offer a warning. If you have a hot air gun/paint stripper that is of course much safer and will usually deliver the necessary heat.