I had to remove the O2 sensor from my 93 Sidekick. I remember employing and old trick I learned from my ex-NAVY boiler engineer father-in-law. Try impact tightening the offending nut/bolt first then try to loosen it. That has worked for me many times. I have used a box wrench and a hammer to do this with good results.

ToyHooter
90 LWB Montero
Sliders, Dual Bouncies, K&N, Flowmaster, Rancho Stabalizer, KYB Gas Adjusts,
ARB Compressor Under Hood, ARB Locker Waiting Garage Floor, Spare Tire Bike/CB Ant Mount

"I didn't do it, you didn't see me, you can't prove it."
Bart Simpson