I just replaced the front O2 sensor which went well but am having trouble getting the rear one out. It appears that I need to remove the plate that bridges the tail pipe and the sensor. Is that correct? I've tried to remove it but the bolts just spin in place. It seems like there are nuts on the back side that have broken free. If I do need to remove, it looks like I'll have to grind the bolts off. If I do this, is it important to reattach the plate?