I have checked the plugs and there is a little deposit...but nothing more than my 300TE had, and she passed the test fine...So I don't see the "cause" of the failure due to the valve stems.

Odometer is broken at 81k miles. I would make the assumption it is no greater than 120k because the head gasket or front timing chain gasket have not been replaced. Not much on this engine has been done. Even the mixture tower has not been touched. Had to grind off the top today to get at the unit.

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k