Ball joint replacement

Tire wear doesn't always equate bad ball joints,though an 18 year old vehicle may very well have bad ones..Have you checked them for looseness,as well as the other steering components,tie rod ends,etc?Alignment could be off as well. Ball joints are either pressed or rivited.Depending on your ability,access to the right tools,you could replace them.A shop will be able to do them so much faster.