I just ran another 1200 miles (much of it through mountains) and Oil consumption is still the same (600 miles per quart). Used 1.5 L of coolant and that has worsened in the last six months and is from the head gasket.

I saw a previous poster who replaced a head gasket and the car had almost no oil consumption after that. I wonder if this might be the issue in many cases.

My theory is that the original engine if extremely well maintained can do well. Clearly mercedes was over aggressive pushing the limits of the block in order to achieve more power for the W140. One should replace Fuel filter and air filter every year, (maybe use cetane boost), rotella t 15w40 (what I've used exclusively this whole time), and last is a big one; make sure your cooling system is modded to keep this engine 95 C and below. Every mechanic says 110 or 115 C is no problem for the block, but you also will not get as much power from the engine likely due to the turbo not putting out as much power at these temperatures. Given its history, you do not want to stress this motor.