Greetings. I used to have that very same issue. In my case I tracked it down and made a change to my regimen that took care of it for me. Previously, I was cleaning up the excess CA on the ends as you stated, before assembly. I believe the problem I was having was due to water infiltration into the blank or under the CA on the ends while I was wet sanding the blank. My new, modified regimen is as follows:
1) Sand the wood blank down before applying CA. I sand down to 800 grit.
2) Replace the turning bushings with the HDPE cone (Non-Stick) bushings.
3) To promote absorption and adhesion of the CA, I clean the blank with Denatured Alcohol and let it dry for 10 to 15 minutes. I don't touch it after it has been cleaned to prevent any skin oil or anything else from getting on the cleaned blank.
4) Use a folded paper towel pad to apply 4 thin coats of Thin CA Wood Finish at 500 RPM (I use Stick Fast) with 90 seconds of dry time between coats.
5) Use a folded paper towel pad to apply 8 thin coats of Medium CA Wood Finish with a short burst of Accelerator/Activator (Stick Fast brand) between coats.
6) Let the final coat of medium dry for 5 to 10 minutes.
7) Remove the blank and carefully sand off the buildup "fingernail" of CA from the ends. I actually do this by very lightly using my disk sander / blank squaring jig to make sure the ends remain square to the tube.
8) Fold a square of paper towel into a pad to act as a blotter, put on a few drops of thin CA on it, and then blot the ends of the blank to seal up the end grain (prevent water infiltration - I think) and create a seal between the end grain and the CA on the ends of the blank (prevent water infiltration - I think). Let it dry or hit it with a quick spritz of Accelerator/Activator.
9) Replace the blank onto the mandrel using the turning bushings to help seal the ends against potential water infiltration. (I suppose I could also apply a thin coat of wax between the bushings and the blank to take this one step farther).
10) Wet sand with Micromesh through all grits at about 800 RPM, wiping the slurry/water off of the blank between each grit. Inspect the blank for low spots, pits, or anything else that might need to be fixed before proceeding.
11) Optionally Buff the Blank if it isn't shiny enough to meet my expectations with just Micromesh.
I use a low speed buffer with the blue buffing rouge from PSI on a sewn cotton wheel followed by a final buff on a loose flannel wheel.
12) Make sure the tube doesn't have any foreign material (glue) inside of it and then I run a deburring tool around the inside edge of the tube. I also use a swab dipped in Renaissance wax (or Versa-Wax) to put a thin coat of wax on the inside of the tube to give the parts just a smidgen of lubrication for when they are being pressed together. I think this also helps reduce the potential for the CA to crack on the ends when the parts are being pressed in. (That was another / different problem that used to have).
I really attribute my success to cleaning the blank before finishing to insure good penetration/adhesion of the CA, and taking care of the CA buildup on the ends and sealing the ends before wet sanding.
Anyhow, that's my regimen and it seems to be working good for me. I hope this might help you figure out what is causing the problem in your situation.
Regards,
Dave
PS Those are some gorgeous blanks!