Agree with this, I used my small mapp gas hand torch (yellow bottle). Mapp gas burns hotter than propane. Get a small 8" ish pipe wrench put a metal tube or your jack handle on the pipe wrench and after getting the o2 bung area nice and hot it should break free. Heat up the area where the o2 screws in because you want that part to expand so o2 comes out easier. Don't forget to put anti seize on the the new o2 threads in case you have to take it out later again.

 

Autozone loan out O2 socket sets. In addition to PB Blaster I have tried Kroil to loosen stubborn nuts and bolts.