You would think that Nintendo would have foreseen all the design issues of the 3DS, well, years ago. The company has been working with clamshell handhelds for over 30 years. However some 3DS owners are reporting that their top screens are getting scratched and some d-pads are cracking.
The common thought in the Nintendo support forums is that most of these scratches are really lines caused by oil and humidity building up when the unit is closed. Users report that they’re easily whipped off at first but become more permanent as they build up over time. Some turn into scratches as well. Users have resorted to sandwiching a cleaning cloth between the screens when closing the 3DS.
SlashGear also dug up a cracked d-pad, apparently the from the same design flaw as the lines and scratches. It seems the rubber stripping around the 3DS is too thin. So thin that the top screen is close enough to the bottom to result in oil build up and a cracked d-pad. Chances are Nintendo will resolve customer issues on an individual basis. Of course most 3DSs are under warranty and most retailers will probably still accept them as returns. Still, if this is happening to your 3DS, let Nintendo know so the full scoop is known and can be properly resolved.