31 00... Information on replacing shock absorbers: Situation
WARNING: This page is about a different car, the 2012 BMW 328i, 2011 BMW 328i, 2010 BMW 328i, and 2009 BMW 328i. 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.