First time I have ever heard of one breaking or even stretching that bad. Like I said before if it makes you feel better replace it. I have 256k miles on my motor and timing chain is not stretched at all. Now when I go to do the turbo upgrade on my motor I will replace it since I will have pistons and everything out ( doing rings) . But until then I will not worry about it . And for a note I change my oil every 3000. miles and I run royal purple synthetic. I dont believe for a MINUTE ABOUT THESE 5-7000 mile oil changes . Oil breaks down under heat and where I live thats all it is is heat and humidity.
Mercedes Technician 7 Years (retired to Hyundai)
2000 Dodge Durango
98 Mazda truck