If you can get access to an impact wrench, that's usually the most effective way to break tight fasteners loose, used carefully.
I find that a 24" 1/2" drive pull bar works best with a block wood to stop blade rotation when loosening these nuts and bolts. Now of course a good strong impact will work but what I have is junk they never develop the Ft-lb torque they claim.
Even with the pull bar you need to use impact rated sockets for their strength and the six point drive.
