I would agree that the cat needs to be as hot as possible, so be sure to run your car at freeway speed for a half an hour before the test. Also, replacement cats are often of lousy quality and will not last nearly as long as the originals, but yours should be ok after one year.

You might want to get a new rotor, and could get by with carefully cleaning the cap, if you don't want to spend a lot of $ on a cap.

Also, a very common problem is plugged EGR tube in the back where it is very hard to get to. The actual EGR valve is usually very bullet proof. There is a great thread on this forum about cleaning this tube out with out taking it totally out of the car. By using a speedometer cable attached to an electic drill, you feed about three feet slowing into the tube from the EGR valve side of the tube to "rotor rooter" it clean. Search this forum for a very good description of this procedure.

__________________
1994 E320 Cabriolet
1992 300CE (Sold)
1991 300SE (Sold)
1986 560SEL (Sold)