Sadly, an empty ink cartridge wasn't the cause, mfryd. I exchanged both black cartridges, switched back and forth manually (via printer menu), performed a number of cleansing operations, but without success. Everything points towards the valve.
Since the printer is roughly six years old, I'll be looking at either a Canon Pro-1000 or Epson P800 as a replacement.
During my darkroom days, I used a Leica enlarger which was decades old, a Leica M3 which was built the year I was born (1954) and, had I not switched completely to digital, could have still been using this hardware. Our digital age seems to require relatively frequent upgrades or exchanges, not only to stay current (whatever that means) but to simply have operating gear. I recall when washing machines or vacuum cleaners lasted far longer than 10 years. Today I seem to need a new one shortly after the warranty expires!
At least my recent cars seem to last
forever.
Sorry for the rant, I got carried away.