Once every year you should return your O2ptima CM to Dive Rite or an approved Dive Rite O2ptima service center for an annual service. This service includes replacement of O-rings, loop hoses, and oxygen sensors, along with a rebuild of the DSV and regulators, and checks of the electronics to confirm correct operation and up to date firmware. This is not a user permitted service. It must be performed by an authorized service center.