Normally they last about 45 to 60K all depending on how you drive and them being mechanically sound. You are due to take a look and lube the guides with a special lube for that application, takes like 5 Min per wheel normally done on a rotation. This keeps them moving freely on the slider and lets them back off fully when you take your foot off the brake. If they bind up, they will wear fast and heat up your rotors and you will have a larger cost when you do change them out. There is a TSB on some models if you are getting a squeaking noise, warranty. MC