After I posted, I looked at the licence plate lamps... both look a little darker than new, so I will replace them today.
I replaced the front and rear lamps with the "correct" sylvania bulbs from Pepboys.
Are any of the instrument panel lights on that circuit, or is it only the exterior lamps that are checked? From my searchs, it seems that if it was a brake lamp. it would only light when braking?
There was also a discussion about the rear lamps and bad grounds/tabs, but I was not sure if that applied to our model..
I assume that it must be one of these bulbs, or the module... where is the module?

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2009 Mercedes ML320 Bluetec