Did you get this sorted out yet? I finally got my Sprinter back from the dealership for warranty work. Mine is a little newer, not sure if yours has the same style headlight bulbs?
Mine has black plastic tabs that hold H7 bulbs. You have to remove/unplug the bulb from the adapter to replace the bulb. I took a few pics that might help?
Turn the large black cover on the back of the housing about 1/8 turn and it should come off.
The light bulbs are held in with plastic adapters with a tab. These also come out with about 1/8 of a turn, align tabs to reinstall.