Problems reactivating Epson SP 4900 after being mothballed in Piezo fluid

Some time ago I went through the agony shared by many of a clogged head. This was eventually solved with a set of Cone cartridges and Piezo printhead cleaning, flush & storage fluid and the 2 manuals procedure recommended on your website. As I was not printing then, I left the printer with the Piezo fluid installed. The printer was functioning well at this point.

I recently wanted to activate the printer and take advantage of Black Friday prices to convert to Cone inks, so I tried a test print, which produced very little. I tried cleaning cycles to no avail, although I got a substantial amount, but far from complete, red coverage when sending an image to the printer. I just discovered that this problem may be caused by the fact that I did not remove the fill hole plugs from the cartridges.

Meanwhile, before I had this epiphany, I switched the cartridges back to the Epson ink cartridges and proceeded with numerous cleaning cycles to advance the ink to the head. The ink did not come. Eventually the maintenance tank filled up, and I am waiting for a new one. Still no test print pattern and a similar result sending an image to the printer.

The situation has left me fearing that I may need a new pump/damper or some other repair (though maybe it is time to replace the damper anyway), and what if that doesn’t fix it?

Or, am I just mistaken about how to charge the ink or how many cleaning cycles it takes? I could not find instructions on that. Some Piezo fluid was going into the maintenance tub perhaps indicating that the pump and damper were working. How would I diagnose whether there is a problem there?

I did not want to invest in a cart of Cone cartridges and inks for a printer that is not fixable or not worth fixing. I would greatly appreciate your suggestions on how best to proceed.

For when it is safe to go ahead with the switch to Cone inks, I would like to know the differences among the HD, HR, and HX iterations. I could not find an answer on the website.