Found on my son's car that the two-piece triangular clamp that attaches the cat to the front part of the exhaust had developed a leak. In fact, two of the three bolts had rotted away. The two pieces are inside a flange on the exhaust, so you cannot get them off. I was unable to get the bolts out and started drilling them out (two are done, one left). Is there an easier way? Is there a some type of replacement part or is drilling the only way to fix?

Thanks.