Front thrust arm and control arm bushings can crack and sometimes tear completely. If this is not repaired quickly, damage to the front subframe unit will occur, which is very expensive to repair. Updated control arms (that prevent damage to the subframe when the bushings wear out) are available.Google+
Car Problem Reports
Mercedes-Benz SL550 Front Thrust Arm and Control Arm Bushing Can Crack or Tear
Mercedes-Benz SL550 Problem
Visitor, 2012 Mercedes-Benz SL550, 26,000 mi
vibration in steering wheel,tires were balanced no change. bushings on both strut rods replaced. considerable improvement in steering wheel vibration and shudder.