This is what happens when they don’t put grease on those parts and it sits for years.
Mild heat, propane, Mapp gas may be too hot, is about your only course of action and penetrating oil. You can make your own penetrating oil by mixing transmission oil with acetone 50/50 mix.
Don’t know anyone who can replace the rubber clutch in the prop. Maybe just epoxy it and let the shear pin do the work if you hit something. The rubber clutch is more important with a gear shift model than a direct drive.