Advice Needed - Exhaust Manifold Leak

The other option is an uneven stud. So the side that screws into the head is one size larger. 3/8” and it is about 3/4” long then drops down to 5/16” with a 2” length. With the un threaded part it’s like 3” long. You can drill out the hole to retap a 3/8” stud. Places like Mc Masters or Granger have them.
Just another option from helicoil. If you don’t like helicoils. I mean what’s not to like- they saved my butt a few times. Just make sure you get the length correct or you bottom out before the stud is all the way in.