QTR-Quadtone RIP

I've been using an Epson 1400 with MIS Eboni-6 inks since the end of 2012. I've used it only semi-regularly in those years and I consider it as having been given light use. The Ebon-6 inkset is the only ink that has ever been through it and it has performed just fine from when purchased until the past few months. I noticed the problem first when I decided to re-calibrate my inkset and noticed a very fine but very regular banding in the 20-70% range of tones on the black ink row and through the midtones of cyan and magenta rows but very faintly. It is related to the printer head as the banding follows the head travel regardless of how I orient the print. I wasn't seeing it in the 21 step tone wedge, however, nor in my prints. That has since changed and now it is often to found in prints but only in certain areas and you have to look for it. But it definitely ruins the print as far as I'm concerned. I have done a couple of full head cleans but even before those the Epson nozzle check was always perfect. I also changed out the black and cyan cartridges for new ones but no change from that. Epson suggested I try printing directly out of Photoshop to see what happened and the problem was not evident when I did that. Up until a few days ago I was using s the 2.7.2.0 version of QTR but I have now downloaded and installed the 2.7.5.0 version. Unfortunately the problem persists. So before I buy a new printer I was hoping someone with more experience than I could shed some light on this issue as I seem to often overlook the obvious Thanks.