Pull the negative terminal off the battery and to remove the exhaust manifold heat shield, you have to unbolt this from the exhaust manifold while the bolts are loosened, apply penetrating oil on the exhaust manifold bolts to soak. Following this, take off the heated oxygen sensors of the front and rear manifolds, together with the EGR tubing from the rear manifold and cylinder head. Nuts securing front, rear exhaust manifold and manifold braces to the block; support bracket; the two nuts at the exhaust pipe/manifold joining. Pull the electrical connector from the oxygen sensor at each manifold, to do this: unfasten the exhaust manifolds from the cylinder heads, and slide them down the studs, the bolts at the rear of the exhaust manifold are extremely tight, you may need a flexible extension for your ratchet in order to get at them. Visually check manifolds and fastener for cracks and damages, it is also recommended to scrape off all old gasket material and carbon deposit from both manifolds and cylinder head. If the gasket was leaking, check the manifolds for warpage on the cylinder head mounting surface by placing a straightedge on the surface and attempting to start a feeler gauge; if the thickness is outside the limit auto mechanics should take the manifold to an automotive machine shop for surfacing. Place the new gaskets on the studs on the cylinder head, place the manifolds on top of them, and screw the nuts overriding them starting from the center nut to the outside. Replace the remaining parts in the reverse to the order they were removed, when connecting the exhaust pipes replace the gaskets and this should solve the problem of exhaust leak and last but not least, start the engine.