Its more then believable. Tons of old Mercedes(123,124,126,ECT) Running at very high miles. Some people just love the car too much to get rid of it 1,000,000 KM is like 620,000 Miles. There is a guy who is Greek Taxi driver who has a 2.8 Million mile on a old 240D.

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2015 ML350 4Matic. Wifes DD
2015 GLK350 4Matic. My winter DD
2012 E350 4Matic. Road Trip car
2009 CLK350 Coupe Designo.Kleemann Tune For nice days/DD
2006 CL600. V12.Eurocharged Tune. Enough said
2005 CLK55 AMG Coupe.Kleemann Tune. For the sound and style
2004 CLK320 Cabriolet. 2005+ Interior swap. For the sunny Florida days & beach days