Exhaust/Cat Converter

[Strife]

I had intended to replace my center muffler on my 380SL because during an o2 sensor replacement (I couldn't get it out even after using both kinds of O2-sensor nut-rounding tools), the shop observed that it "leaked" - and would repair it for $800.

So, I bought the center muffler and the other fittings, seals, and hanger rubber needed. I replaced the rear muffler about 2 years ago, so that was OK.

I cut off the clamp bolts between the CAT and the center muffler, and discovered:

1. The seal was just a little debris on the bottom of the inside of the pipe:

2. the CAT converter flanged lip was partially rusted off.

So, I was a little worried about success, but I put the proper seal and tightened the new bolts/nuts. This (barely) worked, because the car is MUCH quieter.

Unfortunately, when I put some smoke down there to look for leaks, I discovered that the CAT to LH manifold pipe seal is iffy, and even worse, the CAT had a hole in it near a weld. It's small, but still...bad.

So, I have a much quieter car and a strange exhaust rattle has disappeared (basically ,with no seal, the bolts were just holding the center muffler and CAT in "alignment", that's all). This car , with new f/r subframe rubber and motor mounts/torsion rubber, is about as tight and good-feeling (albeit somewhat slower) than my 560SL, which had lived a much more pampered life.

Questions for anyone who has replaced one of these:

1. How "bad" are aftermarket CAT converters? I've read:

(a.) They use hardly any platinum and don't last
(b.) Because of (a.), the engine has to be absolutely in perfect tune at all times or they will be quickly made ineffective anyway
(c.) They are "all" made by the same (crummy) company.

True/False? Any comments?

I am not interested in putting in a "test pipe" or anything like that. And I am definitely not interested in getting an OEM converter (I've heard, 4 large bills).

When I get a replacment, I'll install the new center muffler and put in new seals for the front of the CAT as well as the back. The LH down pipe to the CAT itself looked good, especially after I cut off what was left of it's heat shield