vibration when hitting washboard bumps

When I go over a normal or large bump there is very little movement in my front struts but when I go over a series of bumps, even small ones such as railroad tracks, my steering wheel vibrates back and forth for a second or two. The dealer says struts in front, but I have measured and the height of my car front and rear is on the money. The dealer says that one bump only lets out some of the pressure and the springs hold it but a series of bumps lets out most of the pressure and then the camber is out and causes the wheel to vibrate. Does any of this make any sense and has any one else had this problem. Some said it may be some bushings. If I continue to drive do you think it will hurt anything. Other than that every thing with the steering and handling etc. is great. I dont mind replacing the front struts if they would guarantee that it would fix them. Thanks. Bill