I have had two very good, trusted mechanics, both former lead mechanics at dealerships, tell me, completely indenpendently, do not touch a working unmolested factory chain on a 103 motor. They do not fail. Both said the same thing, the replacement would not be as sound as the original factory work. If it's not making noise on start up - don't touch it. Nothing wrong with replacing the tensioner - it's about a $30 item and quite easy to get to. Anyone who says there is a replacement interval is making it up - it doesn't come from Mercedes.