M157 timing chain

I'm in the market for an E63 M157 car. I'm seeing a lot of 2012's out there probably with the old timing chain. When I do a search on google or YouTube all you get is timing chain horror stories and videos, now I know that only bad news makes it to the internet so my question is how common is the timing chain stretch misfire issue?

Also what's the cost of having the timing chain, tensioners, anti drain back valves installed at the dealer.

Thank you for any information or guidance.