Any ideas on getting a very rusty, very stuck lockring a-loose from a Shimano 7-speed cassette? It's stuck on so bad, when I really leaned on the chain whip and wrench attached to the ring tool, the plates on the chain link where it attaches to the chain whip spread apart, and the chain section flew off it.

No biggie. It's rusty because I FOUND this wheel. Yes, in the trash. The freehub clicks nicely, and the hub bearings are actually quite smooth. So I thought I'd throw a knobby or studdy on it to use as a winter wheel. It'd be nice to get those cogs off, but I'm not gonna cry if I can't.