if your L and R buttons are not working, you do NOT have to send the system to Nintendo. The problem is 99% of the time dirt, and if the following does nothing for you once, try up to three times, and if nothing, then send it into Nintendo, because the problem is not dirt.

To clean the L and R buttons, first make sure your mouth is dry, very dry, then blow into the sides and the top of them, preferably with your Screen closed, so you do not damage the hinges on accident. Blow very hard. This YouTube video does a decent job explaining it, just do NOT use water like some videos state, you can permanently damage your DS by using any water: