Buy a new servo.....Hs81mg requires some dremel work to the chassis but works extremly well. It will also cause some issues with fitting more than seven cells. If you can find an hs56hb it fits with no mods but lacks some torque. It has ball bearings and carbonite gears though. The hs55 is a also a direct swap but the gears are plastic and no BB's. You will also need a servo saver as the losi version will not fit on any of the for mentioned. I have the 81 on one T and the 56 on another and both work well. I would suggest the 81 if you plan to run oversizid tires. The stock servo and saver are proprietary to the losi esc/reciever....Kinda blows doesnt it?