how can i fix my rc car?

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my rc car is cool, but sometimes it doesnt drive backwards, and sometimes it hobbles when i drive foward. also, i called the customer service people and they were some real tard muffins about it. they told me my warrantity expirered yesterday, and that they can't do anything about it... how do i fix this, because i dont know too much about how to assembile a motor and what not. i live in la, california, and i ordered the car from nitrorcx.com Plz tell me what to do or where i can send it to get it fixed