A few weeks ago, I had a magnaflow muffler installed. The installer told me that I had a slight leak upstream of the cat. I have not taken the exhaust manifold off to find the leak yet. I was wondering if anyone has had any luck repairing a crack, if that is the problem. IAP does not have Exhaust manifolds for my car in stock. I am considering headers, but am concerned about whether I would pass smog in California. I am told that there is a performance improvement at mid and high rpm with headers.