I just found out this past weekend that I have the same slight film/streaks on the underside of the protective glass. I.E., between the permanent glass and actual LCD.
It isn't visible when viewed inside a building, or under indirect lighting. When the sun is shining directly on the LCD, the protective plastic cover is removed and there is no image displayed, it is visible.
I discovered this when I removed the plastic protective cover to clean it with a micro-fiber cloth and the sun happened to hit the LCD just right. (I was cleaning it also.)
Not sure if it's worth a trip to Nikon, as it does not affect the viewed images.