Sorry to hear this, not sure how that could happen. not Sure what I would do. I would probably try to tap it and clean up the threads first, and see if I could get the original screw to thread in and torque tight. If that doesn’t work, read up on helicoil products and how to do it - I am not very familiar myself. Just an idea...before you replace the exchanger itself, which I don’t think is very difficult on that year and model. But probably pricey.
