Eastwest, after doing a couple of these HFC installs myself, I can honestly say the demon bolt can be a b!tch to work on BUT, if you have a 24 " breaker bar and the proper extensions, you should be able to either break it free or break it off without the need for impacts! I also used the aluminum floor jack handle extension tube as a breaker bar extension once too.... made it like 4 feet long! Bolt snapped like butter.
Good luck swapping out the O2 sensors, I'm sure that will go easier.
