Most wiper pivot shafts fail due to age, seal damage and lack of lubrication. Factory specs recommends lubrication every 90 days.
Tech Tip: Wiper shaft lubrication is accomplished by removing the wiper arm, gently removing the plastic seal, and applying a few drops of oil where the shaft protrudes from the brass barrel. Switching on the wiper motor with the arms still removed, and applying a few more drops will ensure full and proper oil penetration.