**** WD40, use some PB Blaster. That stuff will break anything loose if you let it penetrate long enough. Spray them with that and then drive the car to heat up the exhaust. Jack the car back up and spray on some more. Use your legs and a long breaker bar to break them free. Heck even if I didn't break the nuts loose I could break the bolts in half if I used my legs. I have strong legs, though.