+1 on the second opinion from a reputable indi.

Not accusing the dealer who gave the estimate of anything but I hear stories about dealers (not just BMW) who try to scare customers into questionable repairs.. Recently I spoke with an acquaintance who is the service manager at a BMW dealership. He was telling me that the pressure on the service department to meet revenue targets at his dealeship has intensified over the past couple years. I think this type of pressure drives the wrong behavior.