I have customers with 150k miles plus with no problems with the timing chain or the rails. The REASON for this is they always do their service. I mean EVERY oil change has been done and the engine was never over heated.
If a customer ever over heats the engine or misses oil changes, the rails will become brittle and the chain and internal parts will be worn.
ASE CERTIFIED MASTER AUTO TECHNICIAN
MERCEDES SPECIALIST 11 YRS