HS55's are the worst servos I have ever seen along with futaba micros.
This are the best you can find at 1/3 the price.
http://www.hobbycity.com/hobbycity/s...?idProduct=662
I always replace std gear with metal one's
.
http://www.hobbycity.com/hobbycity/s...idproduct=6760
Been using HX900 with glow engines for almost 3 yrs with no failures caused by vibration.