As John stated, the impact gun should do the trick. If the threads are stubborn and the cartridge spins free, re-install the forkspring and cap. Flip the fork upside down and push down on the fork while using the impact gun. the spring puts force on the cartridge which helps hold it in place. As for why the guide was damaged......did you install the preload spacers under the spring or on top? If they were installed on top of the spring, they likely shifted to the side and interferred with the operation of the elastomer bottom out system. If they were installed under the spring, I'm not sure why the guide was damaged. Good luck!