It doesn't look like a "crack" to me. It looks as if the two pieces of plastic are coming apart where they are joined together. Maybe there is a screw coming loose, mine has a line there but no gap. Maybe they just became loose did you try and open it too far or something?
That happened to me too. I was like wtf. Htf could that happen. Mine looks exactly like yours.
Poop. I just looked at mine to see if there is a join there, but all I found was a crack...and on the same side as you!ÂÂ However, mine is barely visible at this point.
I guess it's a bit of a design flaw. How long a warranty does this have with Nintendo? How long is a typical store warranty for direct exchange?