If you have some liquid wrench or PB BLASTER, drizzle a couple drops down the shaft into the bushing. Don't use WD-40 as you need a hi-po penetrant. Let sit overnight. Remove the switch from the front end and aply some local heat (soldering iron) to the bushing housing(around the threads) until hot. Then with two pair of pliers one on end of shaft and other where you put heat(but on smooth part), wiggle the shaft back and forth. It should break loose after some effort. Once you get it free, drizzle some sewing machine oil down the shaft. Rotate to distribute.
Larry
Larry