the 380sl also has 2 precats on the pipes going into the engine, one on each manifold. verify if yours has them. there has been some debate on them butI believe MB put them there for a reason and thus when you change the precat, you might strongly consider changing the precats also. the car can run and emissions ok without precats but I experienced a clogged precat and once removed, early failure of a replacement cat. I dont know of miller has a cat for your model, they are also another aftermarket manufacturer.