thanks for all the insight re: hyper flasher.
it turns out it's the passenger side rear lamp: seems to be a combo brake and turn signal lamp. I found the access panel on the passenger side of the cargo area...but...I think I'll have to poke around all the wires and foam sound deadening to see it there is bulb access through the rear of the tail light lens housing...
...anyone replaced a rear brake/ turn signal bulb? is this a DIY project like on any other vehicle? or will this require Mercedes tech help? will removal of rear body panels be required?
