Well.......I had the entire front exhaust dropped to replace the gaskets at the manifolds and to facilitate transmission filter change.

I planning on replacing the front O2 sensors when I started this. I mucked up the rear passenger O2 sensor in this process so was going to swap it with one of the fronts. I soaked them all with PB Blaster several times over this last week.....and......twist it off at the threads. Any suggestions?

 

drill it find an easy out to fit and then heat it cherry hot, install extractor and carefully extract it

or try to heat and somehow screw it in all the way till it falls into the pipe

or drill out the center big as you can and make some relief cut into the threaded part with a hacksaw blade then chisel the pieces inward

or try heating it red hot then drill it and hope the bit grabs it and runs it into the pipe

 

Drill it out as far as you can, then use a Dremel or die grinder with a stone to cut away the ID on one side until you weaken it enough to collapse it with a small chisel. Then you can spin it out. Make sure you dump out the pieces after.

 

If it is sealed I'd just take it to an exhaust shop and have a new bung welded in right next to the old one.