18 40 060 Removing and installing/replacing rear exhaust manifold (M54)
WARNING: This page is about a different car, the 2005 BMW Z4, 2004 BMW Z4, and 2003 BMW Z4. However, it is still accessible from the selected car via links, so may be relevant.
Rear exhaust manifold with catalytic converter can only be removed after front exhaust manifold with catalytic converter has first been removed.
Procedure is described in the Repair Manual headed "Removing and installing/replacing both exhaust manifolds ".