The linkage fails at the plastic bushings and at the ball joints, and the symptom is a wiper that moves slower than the other, parks in the wrong place, or stops entirely while the motor keeps running.
Linkage assemblies are usually sold complete rather than as individual rods, because the bushings are not serviceable separately on most designs. Listings state whether the motor is included.
Wiper arms fail at the spline and at the spring. An arm with a worn spline slips under load and the blade parks wherever it stops; an arm with a tired spring lifts off the screen at speed.
The nut that holds the arm to the spindle should be replaced if it is a locking type, and the spindle should be cleaned of corrosion before the new arm goes on.
