The O-rings of the Underwater cases are  of very soft silicone material, they require  to be periodically washed under running water and to be lightly lubricated exclusively with the grease supplied together with the Inon flash otherwise the O-ring will stretch and deform, losing its original elasticity (thus losing its usefulness)

It must be replaced at least once every 2 years for those who use the case occasionally, every year for those who use the case more than 30/50 dives per year

During periods of non-use it is advisable to remove the o-ring from its seat and place it in a closed plastic bag. If you leave the o-ring in its seat, leave the battery compartment open to avoid crushing the o-ring and subjecting it to unnecessary wear.

A good fotosub always has a spare o-ring with it, it is impossible to find it on an island in the Maldives, but also in 90% of the fabulous diving destinations.