300-400 miles per quart is ultra bad. Its either inhaling it through the valve stem seals(and thus burning it) or it is leaking a LOT. My M103 with 154k on it uses less than a quart per 5000 miles....and thats despite a couple minor leaks. When I got it, it was using around 1qt per 750 miles due to bad stem seals.

At 270k that engine needs minimum new valve guides/stem seals and maybe the valves themselves, and probably several other seals/gaskets replaced. Getting the engine up to snuff will cost significantly more than the car is worth, and thats just to do the engine....

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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)