John,
Are you aware of how the worm and gear assembly works ?
Because your Dec is sloppy ,it means that the worm carrier needs to move closer to the Dec ring gear but the outside grub screw won’t budge due to having so much pressure applied to it from the carriers opposing force. This force may have bent or distorted the grub screw too, however Synta make the grub screw end post out of brass to prevent this.
Below is a link to Astrobaby EQ6 worm adjusting procedures which shows you the logic behind the opposing forces
Most folk have a misunderstanding of how the set up works , it’s sort of reverse logic
Once you get the logic behind it in your mind , maybe try again.Back off the 4 main Dec housing bolts,back off or loosen the inner grub screw and try to screw in the stubborn outer grub screw.
Another thought, get your hand controller and rotate the Dec axis in different positions , loosen housing bolts , try grub’s screw again , tighten housing bolts , move Dec axis again and so on ……
https://www.astro-baby.com/EQ6%20reb...0alignment.htm
Hope you don’t have to pull the mount to bits due to a damaged end block or bent grub screw
Cheers
Martin