O2 sensor

I was wondering if anyone who has changed the bank 1 sensor 1 O2 sensor on a 2001 Buick Century had an issue with it not coming loose and the socket wanting to slip and feel like it wants to round off. I have sprayed PB Blaster on it over and over, ran the car to get it warm and still have same issue. I have the O2 socket the looks like a deep well with section cut out for the wire.

i had to use a torch on mine to get off but be careful with that.

Be absolutely sure your using the right size. If you are then consider using a closed wall socket or box end wrench (6 point instead of 12 preferably) instead of the cut O2 socket. In my experience with really sized sensors the split in the socket will flex ever so slightly (enough to round off the sensors fastener). Short of that torch it like bennuss said. Carefully. Don't heat the sensors fastener but the hole with threads it's fastened in.