I had a couple tech's at my dealer say the m104 is the best engine built. I really disagree and say the m112 to be better, although m104 is easier to work on (inline) vs v6. It doesn't have the head gasket issues of a m104 and oil leaks. The head gasket never goes bad on a m112 unless you overheat it and no wiring issues. They had a crank balancer recall. Some still didn't get fixed. I did one two days ago on a CLK320.

The 722.6 is 10x smoother than a 4 speed and gives you lower rpm with the extra gear and obviously better MPG.

Hands down the w210 is a lot better than a w124. I still love mine though, but the w210 is the car for long trips.

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Only diesels in this driveway.
2005 E320 CDI 243k Black/Black
2008 Chevy 3500HD Duramax 340k
2004 Chevy 2500HD Duramax 220k