In a housing with a groove for the o-ring i would:
- take th o-ring out, clean and grease it slightly
- clean the groove
- put the o-ring back in the groove being very careful to use his original orientation
- don't close the housing, put front and back in 2 seperate zip-loc bags with maybe a silicia bag inside.
Why? Storing the o-ring outside of it's groove may provocate small invisible deformations of the "unprotected" o-ring and/or he is loosing his shape, and this may lead to a leak as the o-ring may don't fit well the groove.
Chris