If the endcaps wont pop out, it might mean that someone glued them in. Try applying heat to the end slowly and see if it budges.

However, when I first got my N20, the outhaul wouldn't budge either. I stuck a pressurewasher nozzle in the slot, closed my eyes and hit the trigger. It got cleaned out... I then bathed the slot in McLube. Now it moves pretty smooth.