Picked up car today. All new parts: Studs, Gasket, Exhaust Manifold with Pre-Cat attached to it.
After picking it up, i disconnected the battery to re-set ECU. Let the re-learning process begin. I'm sure i have been driving for a long time with it leaking. When it leaks, extra oxygen is being entered thru the exhaust, then the O2 sensors reads lean and then the ECU responds with more fuel. I should get better gas mileage now. I am surprised that this did not throw a CEL code.