Power Steering Pump problems of the 2001 Mercedes Benz ML430

On July 14 03 I was driving on the san mateo bridge when all of a sudden I completely lost my ability to turn the steering wheel. I was getting ready to turn off the loop to transfer to the i0i and I had to slow down because the steering was very difficult to turn, luckily with all my strength I was able to turn it and not go over the ramp. I called mercedes foster city and they accommodated me and informed of a power steering clamp defect that can affect the power steering pump (too late for me). . They fixed the problem. On March 19 I experienced the same thing lost of ability to steer luckily I was only on the streets and residential area. I had my husband struggle with the steering and bring it to the plesanton mbusa. They charge me 11134. 74 to repair and not covered under warranty. How does a power steering fail so often and so soon?.