I purchased it new. Used it the first year with no problems. After it's first annual, it seemed to be a bit touchy and was very easy to breath... The second annual and it wanted to free flow when you entered the water. I tried to "thump it" in the palm of my hand, I tried to keep it in my mouth, I tried to hold it inverted, I tried all of the easy in the water cures, including haveing my dive buddy loan me his octopus and turn my air off and then on again to no avail.
I took it back to the shop and asked them to check the pressures and make sure it was set to factory setting.... It seemed to work ok for the next trip and then did it again. I took it out of service and gave it back to the teck to "detune" as much as possible to keep it from free flowing.
I have not used it for a couple of years. I will check the mouthpiece issue as I did use Seacure's on my other Oceanic Regulators due to the comfort factor... I don't know if I have one on the Zeta, I'll have to check. I do have one on my Delta 3 and my Mk25.S600 as well.
I do know that when the problem started, it was all stock...