I found these:
8 Octal Vacuum Tube Keyway Replacement Saver Fix Repair Broken Center Guide-Post
They say: "Put some silicon glue in between the base and saver, let it dry and wipe of the excess glue and you have a tube almost good as new."
Then I see this special tube base glue here:
Tube Base Glue
Any thoughts on the best / cheapest adhesive for the job?