Why would you change that?
In my 45 years of vehicle repair, I have never changed a steering shaft, steering shaft bearing or steering shaft u-joint. I have changed a few rag-joints, however.
Something may be out of round, out of balance, bent or sloppy.
Start with the wheels/tires on a dynamic balancing machine, at a nearby tire store. You think they "look" good? What do they look like while spinning? Maybe a wheel is bent. Maybe there is a tread separation? You can't see that with the car sitting still in the driveway. Maybe a balance weight fell off. A simple unbalanced tire can make tremendous wear in steering and suspension components.
Next, look for slop in the steering system.
Sloppy CV joint?
How many miles are on this vehicle?
How many miles are on your tires? Especially your front tires?