Advice Needed - Exhaust Manifold Leak

Put a jam nut on a turn it out,. install a helicoil without removing the manifold. easy peasy. been done many times. Make sure you use a short helicoil and break the install tab off because the stud goes in deeper until it bottoms. You can take the core plug out in the head to get a look at it from the back side if it is a stud at the front of the motor.