Biggest failure I see people do is having the wiring connected to PCM wiring harness and then when turning the O2s to get them on or off cause the wires to twist around themselves and crimp off that internal reference air path so always have O2 wiring harness free and let them spin as O2 is turning.
Another one (I learned the hard way) is to put the wrong anti-seize compound on the thread thinking it would help by the next removal.
The correct "grease" is a compound that contains glass particles mixed with a sensor safe fluid. Once you start to unbolt the sensor the glass particles brake and free the thread.
If you use a copper anti-seize compound the grease and the copper may come in contact with the sensing part of the sensor changing its properties = slow response + wrong readings.
That's the reason why I replaced my O2's last time...
