WARNING: This page is about a different car, the 2006 Pontiac Montana SV6, 2006 Chevrolet Uplander, and 2006 Buick Terraza. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Inspecting Exhaust Manifold
Courtesy of GENERAL MOTORS CORP.
Inspect the exhaust manifold mating surface for flatness.
Inspect the exhaust manifold for cracks or damage.