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 SL600 Front thrust arm and control arm bushing can crack or tear
Mercedes-Benz SL600 Problem
Visitor, 2004 Mercedes-Benz SL600, 64,000 mi
It seems remarkable that a car with this low of milage would have such problems. The cost of repair is substantual. An expensive car of this make should be built better.