they are re-welding the original weld where it broke off free of charge. he said because I used a "universal" O2 sensor that it must be running hot and the heat broke the weld. He stands by his work. He is a nice enough guy. He also said he wouldn't put the 2.75" DP on and said it was WAY too tight for it to fit and wasn't comfortable doing the job.

I imagine that at some point, I will try and find a shop who is willing to put the 2.75" DP on and also willing to remove the cat at the same time.

They used the factory flange from the stock 180q DP to create the 2.5" and it is stainless, and I know the pipe he welded it to was not stainless, so hopefully he used the right rod for the job.

 

The sensor has nothing to do with it. Your engine shakes to much and breaks the welds. Stiffen the mounts and you will be fine. Just remember that there are about a dozen other people running that dp and no one has posted any problems.