It might be lack of light?
Also, while CCs can handle more watering than most other succulents, it does like to go dry between waterings - not bone dry, mind you, but keeping it continuously moist is not a good idea.

Have you cared for this plant for 30 years, or was it given to you? The reason I ask is that if it was given to you, another reason for the yellowing leaves could be the shock of moving.

Shelly