I changed the serpentine belt, tensioner and idler pulleys on the wifes GLK350 at 150k miles this weekend. I noticed that the ones that came off still seemed to have plenty of life left in them. I roughly determine how worn they are by how fast/long they spin when spinning by hand. My experience with these items off of BMW's are that they spin quite freely after about 120k miles. I'm not going to run till failure on her car because of obvious reasons. What is longest anyone has seen these items last - mileage wise?

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Jim