XAT FTMFW!!!
I have been welding for less than a month and my first exhaust job(also my first tubular weld job) had ZERO leaks.. Its amazing what a fucking wire wheel a flapper disk and some G damn time will do... XAT will get what is coming to them, and good luck getting compensated for what you lost.
Also, Just a shoe in here... You wouldnt of had this problem if you didnt get rid of the 4 cylinder