You didn't mention what you've tried, so this suggestion may be redundant. My trick for stuck components is to freeze overnight, try to loosen, rinse and repeat. I cover the component with cloth to protect it and use whatever tools to hold the stationary part while hand cranking the other. If that doesn't work, I run under hot water, then alternate with freezing. (Obviously don't do this with regulated/computer chipped components!) Typically, a couple good freezings do the trick for me.