I got all the way to the "Rear lamps , High mounted stop lamp ,High mount lamp ,W/o rear spoiler" category in the list, but there was nothing available.
There are LEDs, but they are soldered right to a circuit board, and the fact that they come on at low level, and flicker indicated to me that there is likely a problem not with the lamps themselves, but with the circuit. There hasn't been much in the way of response here, or in the G35 forum, so I guess I will have to call the dealer next week.
Thanks for the try Brian!