Just had surprising bad news from the smog shop
 

They said it had the wrong catalyic converter. I didn't know they cared as long as the emissions were ok.
We bought the car about a year ago from a used car dealer, we bought a car from them before with good results.
So now I get to learn about MB cats in California. Can anybody teach me?

The car is a 2000 C280 with almost 100,000 miles on it.

Yes, another California-ism but I think a handful or other states have the same rules. Replacement cats need a tag visible when installed that indicates California compliance. I had a similar problem, car failed smog visual because of perfectly functioning but not California compliant cats. MB sells rebuilt compliant cats for a reasonable price but not even the MB dealer will guarantee $150-200 core refund until they ship the old cats to some central warehouse for verification. Wrecking yards won’t sell used cats. Luckily I found a private car being dismantled and got the two cats I needed complete with pipes, flanges and O2 sensors for $150. Since they looked and were original, no problem passing. I think your car has 4 cats.

Sixto
98 E320s sedan and wagon

Jim, FYI our local MB dealer sold me a new catalytic converter assembly for our 1998 E320 for $344 with the old core. Since your current catalytic converter assembly is aftermarket, it may not be an acceptable core at a MB dealer. It's a shame that used car dealer routinely cut corners to make a buck. That is why used car dealers have the stereotype poor reputation.

Has to be "CARB" cat. Magnaflow does CARB complaint cats that seems to be good for about 6-8 years and are relatively inexpensive.