Amazing GOOP Auto & RV cures by solvent evaporation, so once it comes into contact with the air it begins to cure/harden.  To limit the amount of air the adhesive is exposed to after use: remove the air in the tube by squeezing product slightly past end of the opening, then tightly recap.  Any product that may have dried in the tip can then be easily removed.  Also, apply petroleum jelly to the tube threads and cap, then store the product in a plastic bag to prevent air from accessing the adhesive.