I now have 5500 miles on my ML320 since my last oil change with the level just fine. I spoke to our local Car talk guy on WOOD AM Radio..
He said I did exactly the right thing. Because the origional owner used regular, there was emmision blow by that deluted and thinned the oil and thus oil consumption.

So by me cleaning the emission control parts, using gas additives, fresh Mobil One and Mobil Premium Gas - I cured it.

He thinks I should change it more often than every 7500 miles however.

__________________
Steve Danville
what i did myself.
CPS
rear shocks
MAS x 3.
SparkPlugs (twice)
Fuel pump & Filter
Window switch
replaced both failed horns with Honda horns.
Cleaned ERG Tube
Oil changes
Oil consumption Fix
Brake Pads
A/C Recharge
Anti-Freeze change X 2.
Front Shocks. Monroe. $90
Mercedes Warrenty Work:
Harmonic balancer,power steering clamp. Cat converters.Drive Shaft Bearing.s
Replaced Outer Lower Tie Rods and front lower ball joints at 156,000 miles