So far every ML owner I've stopped has rust here.

Every ML owner I've stopped has rust starting here or water coming out here (so will have rust, because Mercedes didn't bother to water-proof this latch area). You're looking up into hatch handle, which you can't see except when door is raised. Not exposed to water (unless you dip the entire vehicle in a lake), as it's under a lip of steel trim. Enjoy! 

Note: it's putting out enough water it's rusted the screws

that keep the license plate fixed to the door!