Ditto on the heat, but in that location, you'll need a lot of it! The cast iron pivot will bleed heat away about as quick as it's applied, so use an acetyline torch, and really warm it up. Just be sure there's no accumulation of grease, grass, or anything else flammable to catch fire while you're doing it, and watch out for hot grease squirting everywhere when it finaly lets go. I rehabbed a M-F tractor recently that had the spindles rusted into the front axle, so the steering wouldn't turn. That one took a rosebud torch and a lot of heating to break the rust loose.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!