oil pan problem
 

I had a service at Hyundai dealership that included oil change. A
service advicer called me and said that oil pan plug had damaged
thread. He blamed a shop where I did last oil change. He suggested to
retap and install larger plug. It was done and I was told that it
worked.
Next morning I found a big oil spill on my driveway. I went back to the
dealer. The manager said that unfortunately the larger plug did not
work and suggested to replace pan for about $350. Moreover the pan for
my Elantra 99 is 'a special order' and I have to wait. Then I went to
the local shop where the previous oil chage was done. The
owner/mechanic said it was the dealer's fault. They just wanted to
blame someone else. So, I got in the middle.

Could anyone advice me what to do in this situation? I feel that I have
to pay for the repair as it is impossible to prove which mechanic broke
my oil pan.