i know this is old, but
i ALWAYS pop out the middle pin, AND insulator,
then i solder the +wire to the middle pin, inside the middle pin,
then i solder the -wire to the outside of the connector but inside the connector, lol inside of the outside,WITHOUT the
insulator in the middle,
then when everything is cooled down totally i assemble
put insulator in the middle and seat it correctly, then push the middle + post down in the hole/insulator,
it maybe a pain to get in, but ive found if you put the insultator on the +middle peice its almost impossible to get it seated correctly, so put the insulator in the hole first, it should fit like a glove,
if youse use these extra steps you can heat the part as much as you want, and not ruin the insulator (which is the only part that if you screw up and then you must use a new connector and starts over)