steering probs 99 disco td5

Having probs with the steering,steering feels light and unresponsive at times. Had drop link assembly bar replaced for MOT thats when i noticed the problem,been back to the garage and had track rod ,top and bottom ball joints replaced o/side still not convinced that the problem is sorted although the garage did say that the top ball joint had seized.Just wondering if anyone else has had this problem or can give me some advice on what to try next.