Bearing buddy-type grease caps are commonly clear plastic so the grease level is noticeable. They are designed to be used in a "captive lubricant" hub assembly. Bearing buddies cater to grease fittings in order to top off the lubricant. Grease should be added whenever the sight disc drops below the marked minimum fill line. However, the only way to cancel out contaminated grease is to remove the hub and implement a thorough cleaning, inspection, and repacking of the bearings. It is best to always replace the inner seals and outer retainer while doing this procedure.