Was looking around under the hood of the 320 the other day and noticed some cracks in the grooves of the drive belt. Got a new one and put it on yesterday, with the help if the belt routing diagram in the owners manual. I don't think it had ever been changed in 140K, but I was definately running on borrowed time. I could split the belt apart in my hands.
It is just something you don't want to have to do out on the road somewhere, so take a good look at yours if the miles are getting high.