the capacity in liters is 8.0 which is around 8.4 quarts less than 8.5 or especially 9.0 quarts . if they say it will not hurt, then ask why is there such a warning of overfilling the engine on the oil cap. look at the sheet i have included here, it is straight from mercedes service information, it gives the capacity in liters, your ML has the 112.942 engine and holds 8.0 liters, so the first part applies to you. print this out and take it with you, if you go back, ask to speak with the service manager and ask why have you been over charged and overfilled. i unsestand the 1/2 quart billing, but it should be slightly under filled before being over filled.