This is the reason I use silcon greese... I've left more then one launch with a motor loaded that I wanted to fly and ended up not be'n able to launch it off. ie.. Rain, wind, out looking for a rocket too long, just couldn't get the rocket preped before the end of the launch.. You name it and it's possible. I use Dielectric from an autoparts store, it comes in a nice big tube and cost like $4.00.
Something else to mention while on the subject is about the BP ejection charge. I never load the BP into the motor untill I load the motor into the rocket and that's the last step I do when prep'n a rocket to fly. Now to explain, same as the above about not be'n able to fly the motor. If you have to store the motor over a lenght of time, you want to back off the forward and aft closures to take the pressure off the O-rings. If you have the BP installed then it can get passed the Forward O-ring and cause a failure from an inproper fit. If this does happend what you want to do is, turn the motor upside down and remove the forward closer and assembly, clean parts off of BP grains. Regrease and reinstall.
Finnally, You want to store a motor in a air tight package, I use Boat Box's that have an air tight seal.