31 00... Information on replacing shock absorbers: Situation
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.
When a shock absorber is faulty on one side (leaking, noises, etc.), often both shock absorbers on the axle in question are replaced.