I just tested removing the clutch from my 959 and no problems.
Make sure you're turning the clutch toward you while holding the hand wheel still. I've found that sometimes if you turn the clutch away from you as if you're tightening it, that will free it. Have you tried kerosene or another solvent? You might also try a hair dryer or sitting the machine in a very warm spot for a while.
From what you've described, the hand wheel is disengaged from the shaft and the clutch but the clutch isn't disengaged from the shaft. It could be that the washer is stuck to the clutch and the shaft.