It looks like we have this problem licked. Whether you go to a gunsmith or a machinist, get some experience in your corner.
Ideally it's the heli-coil that was loctited in, and the fastener just broke from fatigue.
I'm not familiar with these rifles. Generally, putting in a heli-coil in an aluminum part is a quality procedure where a fastener requires high torque, or must be removed often. This saves pulling, or wearing out the threads. The rifle may have been built this way, or is a previous repair. Good luck and I hope you are out shooting soon.