1987 190E 2.6 Running Rich??

I recently decided that I'm going to keep my 1987 190E 2.6 benz. I really love driving it, although the wife drives it most of the time. I've been updating\replacing some of the basic tune-up parts and fixing problems. Car runs well, but needs some time and money to bring her back to running like new. Today I needed to replace the muffler, its been a long time coming. I didn't want to spend alot of money so I brought it to a local muffler shop. I'm not sure what brand the muffler that I just bought, but while the guy was replacing the muffler he noticed that the catalytic converter needed to be replaced. He said the honeycomb inside was loose and rattling. I believe him because I've been hearing it rattle too. He said that the car was running too rich, which was why the catalytic converter was possibly damage. I'm not sure if his diagnose is correct and I'm no mechanic. I also haven't been smelling gas. How can you tell if your car is running too rich?