WARNING: This page is about a different car, the 2013 BMW Z4, 2012 BMW Z4, 2011 BMW Z4, 2010 BMW Z4, and 2009 BMW Z4. However, it is still accessible from the selected car via links, so may be relevant.
The following illustration shows the arrangement of the power steering components and lines.
Fig 1: Identifying Power Steering Components
Courtesy of BMW OF NORTH AMERICA, INC.
Check all visible connections, hoses, lines and steering gear for traces of fluid.