I race 1/8th scale nitro on road were the servos are subjected to a lot of abuse and gobs of exhaust residue and spilt fuel during pit stops without problems on my Airtronics servos. Many people have had problems with the Hitec servos(esp. centering) along with some other complaints...

Due to the low cost nature of Hitecs equipment, maybe in combat this can be overlooked. Maybe re-sealing the cases or diverting the exhaust away from them may help and trying to keep the vibration down on the servos mounting point could be benificial. If you're replacing servos often it would seem the savings would not be so great compared to ONE good servo?? just my 2cents.