I think I've got a dodgy rear sock absorber on my A6 avant. The handling seems more wallowy than normal and theres a vibrating patter-patter over bumps. Also oil stains on the o/s rear shock. Need to get it done before we load up with camping equipment and head to Cornwall in three weeks! Are these a fairly easy to diy replace or is it a garage job? I intend to relace both sides together. Thanks..