If the smoke is due to worn rings/cylinder block, then it makes sense that the smoke would increase as you let up on the throttle. When you use a higher throttle setting, there is a higher brake mean effective pressure in the cylinder that pushes the rings against the wall harder. When the gas is let up, then the rings relax a little more and more oil is passed by the rings and into the cylinder where it is burned. This is why oil consumption will be higher at light throttle/high RPM settings.

Before you go jumping to any conclusions as to what may be wrong, how is the oil consumption? I would monitor it if I were you and see if it is acceptable. If not, then you can start trying to diagnose the problem. Usually it is very hard to wear out a Mercedes bottom end that has been maintained properly. You could try a compression test and see if you get good consistent numbers accross the board.

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Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record