Clamp the flat sides on the rear of the gas tube in a vise. Put a glove on and grab the wood part. Rotate it one direction making sure you rotate only and not pull outward on the edges. If it doesn't move one way, try the opposite direction. Sometimes it will move more easily in one direction than the other.
The key to not breaking it is to apply pure turning force as evenly as possible.
Replacing it is the same, pure turning force...