Moisture has helped the clutch disk rust to the fly wheel. To prevent this condition, block the clutch pedal down when the tractor is not in use for an extended period. To loosen, try running the tractor with a pto attachment running & the clutch depressed. It works good if you have a big field to mow. Another way is to run it in high gear & hit the brakes hard. Be careful to brake evenly or the tractor can turn sharply. I would not use a oil based nut loosener on it. An oil soaked clutch will slip easier.