I have not seen one of these just let go. I have had them towed in making alot of noise, knocking and soforth.
I would just wait for the day you hear a slight rattle on start up.
When this happens, you may want to go and get the chain, rails and tensioner done.
Yes, it is a tough job that requires special tools.
ASE CERTIFIED MASTER AUTO TECHNICIAN
MERCEDES SPECIALIST 11 YRS