Wow.... sorry to hear about your problems.
I had the Stone, can't remember which version, that I had nothing but problems with.
Leaking at the bottom where the plastic met the end cap mostly.
Replacing the innards was hit or miss, mostly miss. I finally threw the whole thing out.
I just recently got 2 Viva Novas 2.5.
I bought 2 of them, some 2.8 replacement heads and two purple metal tanks to replace the plastic.
They fit just fine on ProVari and Buzz Pro.
So far, I only have two minor complaints;
One of them leaks just slightly, very slightly at the bottom where it meets the end cap.
And I don't know if it's a complaint or not, but all of my replacement heads read 2. something.
Even the ones that came in the kits.
The idea is there, they just need to get their quality control under control.
It doesn't seem consistent tank to tank, never mind batch to batch.