Monster in the exhaust manifold

[shadowtag88]

I recently had a check engine light and got the error code for the O2 sensor bank one sensor one - on the exhaust manifold

i bought the new sensor today, changed it and in the process i made a discovery.

something had hit the o2 sensor that had gone bad from inside the exhaust manifold. what seemed to have hit it was a piece of metal that was in there SOLID. it appeared that when it hit the o2 sensor, it bent the threads on the exhaust manifold thereby making it EXTREMLY difficult to remove the original sensor. I had expected it would require a few good cranks and for it to come out smooth the rest of the way. instead it was a struggle the entire way out.

once the new one was ready to go back in, the threads on the manifold were slightly ripped up, we took another 02 sensor with good threads and ran that through hoping it woudl realign the threading..
we then took the new o2 sensor and began threading it on, the "piece of metal" in the manifold that we believe hit the old sensor was in the way of the new sensor getting in. we pushed that back a bit with a socket extender and once that was bent back a bit, the sensor went in much more easily. as for the threads, that was still a hassle and the threads were still striped slightly once the sensor was in.

SO-
is there anything that would be heat resistant as well as safe to put around the threading on the sensor to prevent a leak since its not 100% of the way in?

and more importantly, im curious as to what the hell is in the exhaust manifold/ ate my o2 sensor.

any help would be appreciated.
thanks