Most of us would agree that a 99 ML with under 50K (or even 100K) miles should not burn oil at this rate. However, I believe MB policy states that this is an "acceptable" rate. I would go for the district manager meeting myself, they have had some problems with the modular vee engines burning oil, maybe they are "used" to giving in to oil burner owners already. They may ask for a oil consumption test to be completed before agreeing to the repairs.
Gilly