Boy, did you ever open a can of worms here!
I assume you've gotten the service bulletin (letter) sent by MB about changing over to synthetic oil whenever your ML is due for it's FSS service.
We at the forum believe that MB is doing that because they've discovered that the FSS indicator (the little wrench that appears on your trip odometer) was not coming on frequently enough, which means that the oil change intervals were too long (15K vs 5K). Going to synthetic oil, which can last as long as those erroneous service intervals is their cure for the problem.
Trouble is, some MLs may have already suffered piston ring damage as a result of prolonged driving without proper oil change servicing.
If your warranty is almost up, I suggest you get your ML over to the dealership, PRONTO. Whatever the reson for the low oil, is should be serviced under warranty...especially if you are due for bottom-end engine work!!
Sorry for the doom and gloom prophesy, but this topic has been under discussion in earlier posts.
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car