I have seen a number and have fixed atleast one. Most were still in the extended emissions warrantee (70 or 80,000 miles).

The cat is rather cheap, in the $300+ range. They aren't fun to replace but we did it without fooling with the tortion bar.

They are too cheap and too hard to remove to repair by welding as you have found out.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician