VW CC 2010. Catalytic converter was replaced when I first got the car at 78k miles. It is now at 83k miles. Downstream oxygen sensor was replaced at 80k miles. There is a small leak in the catalytic converter.I'm only able to see it because carbon buildup has accumulated in a spray/dam pattern from the hole. Obviously it is leaking exhaust from here but could that be the culprit for a p0420? The other option I have is to replace the o2 sensor I doubt it's the catalytic converter since it's almost new..