TT,
if you remove the front cover you will have some access to the tuning mechanism. Be careful because the speaker is attached to the front and you need to unplug it first. If the plug breaks, let me know and I will point out how to fix it.
Get yourself a can of some type of rust removing penetrating spray with the straw. I like to use something called fluid film. You will find with careful application in strategic places, you can free things up. Then you can clean the excess up with Q-tips and some like methyl hydrate.
The push button rods tend to hang up where they come through the front guide. There is very little clearance there and a little rust can cause big problems.
The tuning knob sometimes becomes hard to turn because of congealed grease in the flexible shaft and worm gear. Also the main shaft has a preload bearing adjustment that can help.
It is always wise to try and determine what is binding. If it turns out to be the tuning cores binding in the sleeves, then this would be the subject of another discussion!
Thanks for your question.
