You really should include all of that information (running rich, etc) in the very first post in the future. That way you will get the best input. If you had said that you were running rich and worked-around it by adjusting air/fuel for example, then that would have triggered different input. I have a 1984 380SL and I bought a brand new Bosch sensor online for $18, same as original. Check what Fastlane here sells it for (see the link above.) If not there are other sites on the Internet that sell them economically like autopartsauthority.com but we should support FastLane if we can since they host this site for us.