Thanks for the advice. I wish I had asked, specifically, that the rails be replaced. I'm extremely disappointed that a MB dealership service center would not do a complete job on such an important component. I would think that MB would have a service bulletin out on rail replacement (as well as all other components of the timing chain package). I would sure like to get a hold of MB's service bulletin on the chain and related components to show to the service consultant. I should have been suspecious because of the cost. The job was done for $750. The same job was quoted at two other MB dealers at around $1,100 to $1,200. I did point out to the consultant that I had read numerous referenced from credible sources that the rails as well as the chain and tensioner shoulc be replaced. He said their experience was that the rails are not a problem if they don't show wear.