Sealed ball joints do not require lubrication as they are "lubed for life" but standard ball joints must be lubed from time to time. It's best to inspect standard ball joints once a year. Generally speaking, standard ball joints will outlive sealed ones because eventually the seal will break, causing the joint to dry out and rust. While there is no exact lifespan that can be put on a sealed ball joint, they can fail as early as 125,000 miles. Signs of a failing ball joint start with a clicking or snapping sound when the wheel is turned and eventually turns into a squeaking sound at the end of a stop, when the gas pedal is used and/or also when hitting bumps. Please note that if a ball joint fails, the results can be dangerous as the wheel will attempt to fall off the vehicle, causing one to lose control. Because the tire will be at an odd angle the vehicle will come to a screeching halt, damaging the tire. Also, during failure debris can fly out at orbital speeds, damaging other parts of the vehicle. When there is evidence of a failing ball joint it is best to avoid pot holes, especially at high speeds, as these will cause stress on the ball joint. wikipedia.org
