I would recommend going to your LHS and buying a good servo. Most unheard of brands most likely have ripoff things that are bound to break. With a servo from a known brand (JR, Airtronics, Futaba, etc.) You will get a servo that will last longer. If that doesn't solve it than I guess that you are setting your endpoints too far and the servo is working so hard to get it to the end (Where it can't go) that it'll just die out.