both are giving lame excuses. iridium plugs last very long. Xulfiqar bhai mentioned how long.
secondly, wd40 will not affect the plug system.
any bolt will tend to sieze when it is not opened for a very long time, heat cycles will further promote this. engines are expected to run hot and the tightening of bolts as a result is normal. it is not due to overheating. it is normal.
it is good practice to apply antisieze to prevent this. i am not a user of iridium plugs so i can not say for sure whether all brands come with antisieze applied or not.
anyways, you can expect a plug to just sieze after such a long time period. esp if it didn't have antisieze.
try wd40. just keep it away from rubber and plastic. wipe off with a cloth before reinstalling the wires/coils
spray it on , leave it for a few hours, try again.
people like to see the colour of the spark plug to know whether the engine is running rich or if the plugs are fouled. but it is an outdated method, if you are getting decent economy and performane, you don't need any "tune up".
as for the gapping part, try to find some info from ngk or denso about it