Glowforge stated they would change them for a minimal cost when the product was announced and the first units shipped, but over time that was gradually phased out - to the point where the original posts here discussing it and FAQ statement were subsequently deleted. I had the wherewithal to take a screenshot on Dec 20, 2020, showing that statement.
That statement also said the tube was rated for two years, and a replacement “kit” would be available, but that never materialized either.