31 00... Information on replacing shock absorbers: Situation
WARNING: This page is about a different car, the 2013 BMW X5 M, 2012 BMW X5 M, 2011 BMW X5 M, and 2010 BMW X5 M. 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, limit values exceeded on the shock tester), often both shock absorbers on the axle in question are replaced.