If you spend any time wrenching on 'peds, you MUST have one of those impact drivers you whack with a hammer.
With Liquid Wrench or my friend Rust Buster and the biggest hammer you can get, you can loosen most any screw.
And the biggest hammer part is no joke. I've seen people tapping an impact driver like they're driving a nail. The secret is to get the biggest hammer you can and give it a good whack while holding the driver in tension in the "unscrew" direction, depending on if it's a right hand or left hand thread.
Surprisingly, you can do more damage with too small hammer than too big.