I have 2 pens here that appear to have the sections glued to their barrel. Both are lever fill.

I say appear because I can't unscrew / detach them so I assume they have been glued & I don't want to use too much force & end up breaking something.
At the moment I have no real need to detach other than to inspect the ink sac, but at sometime in the future I will need to replace the sac.

What is the likely glue? would this be shellac?

Why would this be done in the first place?

What is the best method to seperate? ~ if its heat where should this be applied? I assume the barrel, but would soaking in warm water be useful?

Many thanks

Do not soak a pen in hot water, sometimes they can warp and deform. A Hairdryer can be useful for applying heat. If you are dealing with old celluloid, it can spontaneously burst into flames if heated too much. Heat should be applied to the section/barrel joint.

If your hand begins to feel as if it is burning, your pen is too hot.