Oil seals are a common way to reduce bearing contamination in machine tool spindle applications. They are used primarily in low speed applications because they make contact with the rotating shaft and have a limiting surface feet per minute specification. They do eventually wear down. This wear is increased if contamination migrates into the contact zone. Grinding swarf is a good example of this. The rotating shaft can also be worn when this occurs. The shaft wear can be repaired with a grind plate grind or the installation of a speedy sleeve.