My X5 went for regular maintenance service last month and my service advisor told me that my X5 needs serp belts to be replaced. He said three of them need to be replaced and the total cost including labor would be $390. Let me know if this is reasonable. Also i think it should have been included in maintenance warranty (which i still have). What do you guys think? What are Serp Belts and should they not be included in maint. warranty?

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2005-4.8is