Such corrosion can result in abnormal wear of the joint, resulting in separation of the joint. Loss of steering control can occur increasing the risk of a vehicle accident.
The pitman arms were not fully lubricated at the assembly plant. The "ball joint" at the outer end of the pitman arm can become contaminated and corrode.
Dealers will inspect the vehicles and if the joint is found to have significant wear, the arm will be replaced. Those pitman arms not replaced will have the "ball joint" fully greased.