I was always told that using a quart of oil, in 1000mi or less, was considered "burning oil". So, it looks like you are inching your way towards that mark.
Of course, before thinking engine rebuild, you can externally check out the engine from top to bottom, just to make sure your not loosing your oil through leakage. Sometimes oil can get dragged long the chassis a ways before being flung to the ground.
btw I think that many owners (not neccessarily Benz owners) would be very happy to have an engine with 200k and using 1qt. of oil every 1500mi.