RE: JR servo gear train problems
I use both the 3421 and 3421SA (plastic gear). I prefer the SA because the metal gears wear faster. My biggest problem is that I have not been able to get replacement gear sets for a long time. The estimated availability date keeps moving. So, you may have problems getting these servos.
These servos are popular with pylon racers. If there was a problem, I don't think they would be using them.
This little servo is expensive but amazing. Once you have used some, you will be hooked.