I looked inside one of the servo motors (Y axis). Inside, I was surprised to see a circlip (retaining ring) and a setscrew. It is as if the encoder shaft was inserted into the actual motor shaft and held by a setscrew. Could that be true? If it is, I could make any encoder shaft, as long as it could fit inside the main shaft? Are the brushes in good condition, or do they need to be replaced with a new set? I knew that the incandescent lights in encoders (which cause all kinds of troubles) need to be replaced with orange LED lights in order to be safer. Ultimately I replaced the encoders altogether.