Toyota Repair: Toyota Exhaust Manifold, o2 sensors, judgement call

Question
I have a 1999 Toyota Sienna and I found out that my O2 sensors went. While replacing the O2 sensors the mechanic stripped out the threads that hold the O2 sensor. I do know that this was for the most part because the parts were rusted. Is it going to be my responsibility to pay for a new manifold since they can no longer get the O2 sensor to stay in? Is it the mechanic's fault?

Answer
We run into this frequently, this happens because the threads get rusted over time and by removing the sensor the threads can get stripped in the process, I don't see how the mechanic could be blamed but on the other hand if the sensor is hard to remove we normally notify the customer that a new manifold may be needed and ask the customer if they want to procced knowing this, the customer then decides whether to go ahead and take a chance or stop the repair. It's a judgement call, talk to the management of the repair facility to see if they are willing to assist, how about you pay for the part and they do the labor at no charge to you.