The valve seal is a piece of ¼” Teflon rod 1/8” long with a 1/8” hole drilled through the center.
Teflon is soft and deforms easily, so I drilled to a depth of only about 1” length at a time. I was concerned about the drill drifting off center in unsupported material.
Then I used a small saw to cut the 1/8” pieces.