I am first assuming you are talking about separating section from barrel on vintage pens; true?
20% seems excessive in my limited experience (standard disclaimer - I'm not a professional restorer - strictly work on my on pens, but with over 10 years experience).
The key may be "... then god knows.. getting more and more reckless as my frustration builds!"
The first rule of pen restoration is patience - as well as the second rule.
Heat is your friend, but dry heat at around 140 degrees F; this is sufficient to soften shellac and "relax" the plastic. Wet heat risks clouding celluloid and discoloring hard rubber. Dry heat from a source such as a heat gun or hair dryer works best - but know what temperature with which you are working.
Buy or make some decent section pliers - search around these parts and you will find a source or check out your local auto parts supply and look for spark plug pliers (don't know what they are called in the UK). You can accomplish the same thing by grinding the teeth from a pair of slip-joint pliers and covering the jaws with short bits of poly tubing.
Did I mention patience?
You have to heat the barrel threads sufficiently but not to the point you scorch, shrink, or ignite the material - thus the 140 F temperature target. It may take several cycles of heat/cool to loosen the section and you will need to apply gentle force to the section - gentle being the key. If you become frustrated, put the pen down and take a break.
Read Ron Zorn's (www.mainstreetpens.com) Articles and Essays section for tool and general advice - pay particular attention to the article "Seeing With Your Fingers."
May we live, not by our fears but by our hopes; not by our words but by our deeds; not by our disappointments but by our dreams.