I did this too, but had the local muffler shop heat and rebend the header ($100) and popped in a new Upsteam sensor, dont care about rear one for now, no testing in my area for smog or whatnot. Nice $150 fix =)i had a similar problem. my o2 sensor was going off and even after i replaced them i drove it for a few days and it would go off again. come to find out that the exhaust mainfold was bent (had been run into a curb). it had pushed the exhause manifold and headder back and was causing the wires to overheat and set off the sensors. cost me 1500 to replace the header and manifold and put new o2 sensors in.. and i have not had a problem with it since.