It certainly sounds like the "stealer" wants to get some $$ out of you.
I have never heard of such bull#$% before.
"Oil consumption test kit"? ........please.
Do yourself a favor, pull your plugs out. If they are oily, then you know something is wrong and oil is getting there.
"MB dealership wants me to bring my car in to install an Oil Consumption test kit on my car"
Did you tell them your car is consuming oil?
If it is, what is the rate?
If not, why in heaven do they want to install an "Oil consumption test kit"?
(please provide me with a picture of that thing, I am dying of curiosity here, if not laughter)