Sorry about your trouble.Mine has done this to me about 4 times but i have a futaba servo in mine since i bought the kit. You have more than likely stripped the gears, and it is not a real problem to fix. Dont you have a duratrax mt.If you do, then the servo on that might work in your stampede. Check this out for some decent metal geared servos.
http://www.misbehavin-rc.com/pit-lan...o/es-servo.asp
Out of thes i like the cirrus cs-60 and cs-80 metal geared servos best for the price, and i would like to get one myself sometime. I know you just bought the truck and that your aggrovated that its already broke, but things like this will happen. I dont think you would have got a lemon or anything either(hopefully). Breaking the steering servo in a stampede is a common thing though, but i think you could fix that with one of those metal geared servos.Good luck.