Fine threads plus extreme temp!
Easiest way to remove it with limited stress is to get your box end wrench out and with one hand hold it tight and use a rubber mallet or other similar tool and gently tap repeatedly on the wrench until the bolt breaks free. Remember to tap, do not wail on it!
I thought with my stock Y-Pipe out of the way it would get easier with a 3/8" socket. NOPE!
I have to do this everytime
