There are 5 fundamental problems with AGFrc and their re-branded servos that I am currently aware of:
1) The potentiometer is glued in place with silicone and the silicone degrades over time where the POT will slide out of place from under the main servo spline gear, I used CA glue to re-attached my POT. The symptom is when the servo no longer centers. You can either wait for issue to occur or use a better quality glue as a preventative. In a perfect world the POT should be secured with fasteners which is what I believe is done with NitroPro upgrade
2) The servo motor is also glued in place with silicone and will slide out of position which causes the pinion to slide off the motor shaft and loose mesh with the first gear in the gear box. The symptom is grinding sound where the servo may work under no load but will grind under load. This can be repaired by using a tap to reset the pinion onto the shaft. NitroPro has improved the design to where I believe they use fasteners on the motor and they include a special lip over the shaft of the motor to prevent it from sliding out of place.
3) The 1.6mm pin which aligns all the gears will tend to snap over time, NitroPro is experimenting with a softer metal to let it bend instead of snap. I have made my own pin with a body clip and that seems to be holding up better. The symptom of a snapped pin is the servo arm locks up when power is turned off. Always check that the servo arm moves freely after every run with the radio system off.
4) If the pin has snapped the servo will still function without any other warnings, but you risk bending the shaft of the servo motor because the gears will be wobbling around without the pin to keep everything aligned properly. Once you bend the shaft of the servo motor then it's damaged beyond repair... this issue exists for both AGFrc and NitroPro branded servos.
5) Slop --- After fixing the pin with a flexible body clip, then the aluminum case will start to wallow out around the slots which hold the pin and this creates excessive slop, this issue exists for both AGFrc and NitroPro branded servos and was the final reason why I switched brands of servos
I have only addressed what NitroPro has done to correct issues above the base model AGFrc servo, I did not inspect any other of the handful of rebranded servo that are also based on AGFrc servos.
I question the integrity of AGFrc but have been very impressed with all the hard work and support that is offered by NitroPro on improving the quality of AGFrc based servos, I believe NitroPro will get all these issues resolved soon