Had a HE__ of a time getting the last O2 sensor out that I needed to replace.
Soaked with WD40 and PB Blaster about 20-25 times over two weeks before trying to get it out.
Still had to heat, wrench, and work like crazy to get it out.
Brought 1/2 the threads from the bung with it.
Re tapped enough to get new one in and tight but it was work.