The retired electrical engineer has only watered the plant twice, the last time in 1972 when he oiled the plastic stopper so that it wedged so tightly it hasn't been out since.
Indeed - a reason wine bottles have a capsule in addition to a cork is to control diffusion.
The diffusion rate through the cork should be quite small, but might serve to help equilibrium. It's an inspiring thing to try... the plant of the long now.