I've thoroughly searched the forums and can't seem to find a definite answer to this question. I purchased my '98 S420 a few months ago with 118,000 miles on it and I don't know if the timing chain has ever been changed. What is the recommended interval for timing chain replacement on this engine? Should the guide rails be replaced as well?

I know a rule of thumb on the 126 V8 S-classes is to change the timing chain and guide rails every 10 years or 100,000 miles, but those are the 116 and 117 engines.

Since a timing chain job is beyond my technical capabilities I would have to have a shop do it. Any idea as to what it would cost?