I have little knowledge of those machines so this may be more a thread bump than useful. What I do know is a couple of generalities of clutches sticking to pressure plates in long term storage.
1) If you can figure out how to apply a load with the engine running and clutch depressed, you have a shot at breaking it loose. As an example, many tractors will start in gear if the clutch is depressed. Chain the tractor to something such as a stout tree, start it with the clutch depressed, and there’s a decent chance it will break the clutch loose from the pressure plate. If it doesn’t work, the tractor either bogs the motor or spins the wheels, but no further harm done. If you can figure out something similar on your machine to create a load with the clutch depressed, yet not risk further damage if unsuccessful, I’d do that first.
2) Tear it apart. Do whatever you have to do to pry the clutch off the pressure plate. Inspect them and replace if damaged.
3) Going forward, when storing equipment with a clutch, it may be worthwhile to rig a block, stick, clamp, something mechanical to keep the clutch depressed to keep it off the pressure plate so there’s no potential for sticking.
