Pierre
Fellow
I glued mine in. I just used a little bit of epoxy on the end of a toothpick to coat the inside of the hole - but no more. I left it a few minutes to get tacky, then pushed the ferrule in. Didn't seem to have a problem with the glue seeping in (I tried a nib in it in a few positions and it seemed fine).
But didn't you glue yours into a 6.5 mm hole in an acrylic blank instead of the brass tube?