Epson has a fluid it uses for cleaning and storage. You'd need to ask an Epson tech about availability. AFAIK, it's not on the market. I was going to use it some years ago, and heard about it from the company that services my printers. It cost about twice as much a Piezoflush, at the time, but came with assurances from the Epson tech that it was exactly what I would need for long term storage. Needless to say, he was down on Piezoflush.
In the end I used Piezoflush over several storage cycles with my first Epson 9900. Eventually the one channel of the head gave out. I can't say that was because of any compatibility issues with Piezoflush, despite the tech's warning. 9900 print heads are notorious. On my other printer, a newer 9900, I have avoided using it so far.
// Paul