2003 Mercedes S500 sedan with 126,000 miles in the United States Md.

In spring 2012 I had the motor mounts replaced by a Mercedes dealership and about a month later I noticed a clicking noise from the left front of the car when turning and then 4 months later it got worse and more frequent. I took it to a Mercedes dealership for service to address this steering issue and the advisor said it needed a new rack pinion steering. I am curious to know if it is possible that when the motor mounts were replaced that the rack pinion steering was damaged in the process of the replacement of the motor mounts? Also, could you please explain how motor mounts are installed and how/why does rack pinion steering need to be replaced basically what could have caused the rack pinion steering to fail? I have owned 4 Mercedes well into the 150,000 mile range and have never had to replace the rack and pinion steering. Also, the car has never been in any accidents.