Most Subaru ball joint failures result from one of three issues: normal wear and tear, impact damage, or contamination. The ball joint is a high-stress part that wears out with regular vehicle use, especially if driven on rough, gravel roads. Slippery winter road conditions can lead to impacts with potholes and curbs. If the ball joint's protective rubber boot becomes torn or cracked, dirt and water can enter the joint, contaminate the grease, and cause corrosion and rapid wear.