I read this article:
sludging issue shortly after I got my 07 E320 Bluetec. I am not sure if I can be of any help, but I have been running Mobil 1 ESP (not sure if it is .51 or .52) oil in it, and changing at 5K intervals. The article focuses on the Sprinter, which can be considered more "severe duty" than a sedan or your ML. I believe your ML definitely needs the ESP oil because of it having the AdBlue system. My '07 does not, but I am running ESP oil anyway. Again, probably not much help, but that is my experience.