Aside from the poor tensioner design and brittle plastic, these M62's run at very high temperatures which contributes to the plastic degradation. The S62 engine has a very similar chain guide design and failures are quite uncommon, mostly because it uses thicker oil and runs at a significantly lower temperature.

That being said, it's a total crapshoot. My X5 4.6is lasted until 213k miles on original guides with the original tensioner, meanwhile others have had chain guide failures shortly after hitting 100k miles.

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2003 X5 4.6 | 2000 540i Touring

Formerly owned:
2004 Range Rover | 2000 M5 | 2000 540i/6
1995 750il | 2003 Mercedes S500 | 2003 540i/6