I have brought two printers back from the dead - a 3800 and, recently, a 7880. Both of them had sat unused for extended period. PiezoFlush was important in cleaning out stuff that was clogging the head, but both had ink tube problems too. These were harder to identify. The 3800 had a slight air leak. With this, I could get a perfect nozzle check immediately after a head clean but a second nozzle check shortly after showed gaps. These got worse with subsequent nozzle checks.
With the 7880, I replaced the dampers before doing anything else. The ink deposit in the Magenta damper was noticeably different to the others. There was less ink and it seemed dryer. With hindsight I should have paid more attention to the ink tube straight away, but access to the other end of the tube was more difficult than just re-tightening the tube and trying to flush it.
It took very little flushing, through head cleans and a few power cleans, to get perfect nozzle checks on every colour apart from Magenta. This encouraging result led me to the bigger step of getting access to both ends of the ink tube and rigging up a flushing system. The internal diameter of the 7880 ink tube is 1.8 mm. I was subsequently able to purchase a needle with an outside diameter of 1.8 mm from a medical supply company (I already had some 60ml syringes to use with it), so I have a better system for flushing an ink tube if the problem arises again.
I mentioned all this because I have often seen the logic expressed that if replacing dampers doesn’t fix a problem then the next step is to replace the head. Checking the ink tubes is a cheaper next step, but if the tubes are clear then the head must come under scrutiny.