Yeah Rusty, both ball cups AND studs can wear, and need replacing once in a while. The steering on the 'vader is notoriously sloppy. You can tighten it up a little, by replacing every stud and cup between the servo and the wheels. The Vader uses a fairly standard size ball cup, RPM makes good ones.
I've also had to replace a-arms over time. Like you said, anywhere there's a hinge.