I've got an 87 420SEL with 107K on it. Had put off doing the chain and guides for longer than I felt comfortable and finally had them done two weeks ago as my mechanic (Mitch Carr's in MD) said that they recommend 10 years or 100K as they were seeing too many guides break past 100K. My rails were dark brown and several had broken already but fortunately no pieces had dislodged -- they all had nice deep grooves etched into them. Mine was quiet as a mouse starting hot or cold. I agree with blackmercedes -- at minimum, get someone who knows to check it out. As I see it, when the alternative is $4K+ in valve damage (maybe more than the car is worth) getting it done in your mileage/age range seems to be money well spent.

John

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04 C230K Sedan
01 Boxster

00 C230K Sedan (sold)
87 420SEL "Phatryd" (sold)