No oil stain, but it probably is running a little rich because it isn't breathing too good considering it's around 7 years old and looks like it has never had an air filter. I just inherited the mower, and I'm probably going to send it back on it's way soon. Just had to play a little. The exhaust doesn't need cut to do this, just unbolted and the tubes slide out of the muffler, and turn them 180* and bolt them back up.