O-Rings (pack of 5s)
The o-rings in the balls of the adapters/arms will last one to two years if not left out in the hot sun all the time. They will crack, but this will not affect the clamping ability of the clamp. They should be changed when they are cracked, hard or the arms do not seem to be holding as well as when new. They can be difficult to remove.
Squeeze with thumb and forefinger and push to one side, this should give you a small amount of rubber to then roll over the ball.
Take the o-ring and stretch it over the ball and into the groove. If you lose the o-ring while on a dive the clamp will still work; but you will have to tighten it a little extra since the o-ring is gone