The 4matic doesn't impact the mileage that much. My 4matic c-class wagon gets about 20-21 around the city and 25-26 highway....its a simple but very effective full time all wheel drive system. If you keep all the fluids changed and good then it will easily do 250k.

A good test for a 4matic model is to do some slow tight turns and feel for any shuddering. Shuddering means transfer case = ?? or might just need a fluid change. Even mine with 132k was not shuddering with original fluid and I had it changed when I bought the car because I wanted it to be good for a while. Everything is smooth and the 722.6 Transmission is amazing.

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-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)