Focus lost on locking cause

I HAD a problem with my Ford Focus locking the steering while driving. You helped me contact Ford, which replaced the steering column and lock. But last night while I was turning at a major intersection it happened again and was quite scary. The steering jammed completely and I had to turn the car off and on to move out of the way and the truck behind me almost wiped me out. I have spoken to a Ford dealer who is willing to look over the car at my cost. The problem is they don't know what they're looking for or what they might have to replace. I'm really struggling over what to do next.