I have an ongoing issue with emissions on a '98 Z3 with a non-factory supercharger. Took it in last week fully expecting to have to replace the catalytic converter as the car was throwing a P0420 code. Turns out that i had a bad valve cover gasket that was allowing oil to leak into the spark plug wells. After they replaced it, the car passed emissions straight off. They could have replaced the catalytic converter and i would have been none the wiser. It is a testament to their integrity that they did not do more than was required to restore my vehicle to service. there are a few non-critical things that could stand some attention and, when the time comes to address them, i won't hesitate to take my vehicle back to them for these repairs. Helpful staff that listens respectfully and explains problems fully.