Can anyone tell me what the part circled in red on the photo below is? It's on an 83 380sel that I just had a custom cat back system installed on.

After everything was all buttoned and sounding great, I discovered there is very small leak coming from somewhere near the top of it. The outside is surrounded by a sheet metal shield and the oxygen sensor screws into it. Thanks.

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2000 Mercedes S500
1990 Mercedes 560SEL
1970 Triumph Spitfire

Thats the front cat pipe.

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1980 500SE/AMG Euro
1981 500SEL Euro
1982 380SEL
1983 300TD
1983 500SEC/AMG Euro
1984 500SEC
1984 300TD Euro
1986 190E 2.3-16
1986 190E 2.3
1987 300D
1997 C36 AMG
2003 C320T 4matic

past: 1969 280SE 4.5 | 1978 240D | 1978 300D | 1981 300SD | 1981 300SD | 1982 300CD | 1983 300CD | 1983 300SD | 1983 380SEC | 1984 300D | 1984 300D | 1984 300TD | 1984 500SEL | 1984 300SD | 1985 300D | 1986 300E | 1986 560SEL | 1986 560SEL/Carat | 1987 560SEC | 1991 300D 2.5 | 2006 R350

It is a cat and the second one is also a cat. In other words it has 2 cats. However when you look up the parts they are considered one part.
paul

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84 500 SEL (307,xxx miles)

If there is a leak you need to take it back and get it fixed. It might be leaking where it connects to the manifold. Or could be a defective part I suppose.

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

I chose to have a custom cat back system fabricated because parts of the original system had been cut off (including the back flange on the converter) and everything was welded back together. The pipes were still in pretty good shape and it was determined that the converter was still good, but both mufflers were totally shot.

I've used this shop before, they do good work and are very reasonable. I figured as long as the converter was good their plan of bending all new pipes and installing new mufflers at a cost of less than $300 was pretty good. Then, if the converter failed later I could have them splice in a universal at about $500 less than one made to fit.

At this point my question is this: Does this front "cat" actually have catalyst in it, or does it just provide a place for the oxygen sensor?

The car is back at my regular independent shop and they are wondering if they can remove sheet metal shield, and assuming there's enough good metal, find the leak and weld it up without hurting the car's ability to pass emissions, which it now does with flying colors. Any ideas?

Thanks.

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2000 Mercedes S500
1990 Mercedes 560SEL
1970 Triumph Spitfire

I wound up taking it back to the muffler shop. They removed the heat shield and welded up a 2" long crack in the first converter. I then took it back to my regular shop and they put their emmisions tester on it and it was still good. BTW, the muffler shop says they could see honeycomb through the crack before they welded it, so there is catalyst in it.

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2000 Mercedes S500
1990 Mercedes 560SEL
1970 Triumph Spitfire