I disagree with gas engine vibration stripping a throttle servo, at least not when the servo is back in the fuselage and you use nyrods or the Dubro flex throttle cable in a tube that I favor. I also use IBECs in all my gas ignition powered models, so I have an alternate method of killing my engine in the case of a throttle servo failure. Any servo can fail, I know, I lost my beloved Goldberg Extra 300 to a servo failure. I had just swapped out an original aileron servo the week before the crash, since the old servo started to get jittery at neutral due to a worn/dirty pot. I put a NIB servo in off the shelf and put one in that suffered an early life failure of the electronics. So much for trying to be pro-active with the maintenance
I will agree that MG servos are probably the best bet when mounting the servo near the engine with a heavy unsupported metal linkage that can vibrate or resonate violently at certain engine RPM's. I just won't go that route when mounting my throttle servos for gas engines.
I also think that keeping the throttle spring engaged acts to bias, or damp out some of the vibration on the gears.
Pete