I checked for Mares12 III. Its older then most of us on earth. That’s back when Mares is basically a Dacor. Dacor parts will work. But why ? Your 2nd stage is about 30 years old. Just get a another lightly used 2nd stage that’s 20 years newer for the Mares 1st stage. The kit for your 2nd stage is discontinued. And the shelf life is about 5 years for the kit. If your still diving after all of these years then you deserve going to a dive shop and getting the cheapest that would be a lot better then what your using. Take care