I can't believe that a company with the reputation Losi has would ship an ST without a servo saver. You probably already have one in there.
A failsafe is a must-have. I ran an Ofna micro failsafe in my GT, and it works great. Just remember to secure your battery pack and route your wires safely around the engine, 'cause if you lose power the failsafe won't do jack for you.
the springs work becuse when i tested it from wot and turn the radio off it closes the carb
If the crystal just fell out the servo was probably still getting a signal to stay at WOT. There's no TRS that could fight that, but a failsafe would probably have saved it.