This has happened to me with every model of DS I've owned and if it's like my problem it's just dust stuck under the shoulder buttons. I can usually get by with just blowing air under the L and R buttons. Replacement shoulder switches are available from some other websites but you have to solder. If you want to do that you should be able to just follow the steps in the [guide|1300|back panel removal guide] to access them. Then remove and replace.