One problem related to steering pinion shaft has been reported for the 2008 Mercedes Benz CLS550. The most recently reported issues are listed below.
I was driving g through a parking lot when the serpentine belt broke. Naturally, the car became difficult to steer but manageable. As I attempted to turn into a parking spot I heard a 'pop' under the hood. When this occured, the wheel went into a free spin. There was no input from the steering wheels to the rack and pinion. Upon investigation I found the lower steering shaft broken about 2 inches above the rack spline. The steering shaft was broken in two. The increased force required to turn the wheel was too much for the shaft to handle.