You need to speak with a different tech then, I would call that bad advice. Print adjust simply doesn't affect the way the ink flows through the machine. Kinda like fixing a flat tire by changing the oil. We only do a print adjust when a head is changed. You could do one every few months for good measure I suppose, but I don't really see that needed either from my personal experience.
There is alot of things you can check for the ink starving issue. First I suggest doing a search because this has been discussed before.
What resolution are you printing at? 360x540 4pass bidir, I wouldn't be surprised if you are getting this issue. I believe high flow dampers are recommended if that is what you are running. We ran at this resolution for a brief time and found the trade off on quality wasn't really worth it (banding). On the other hand if you are at 720 8 pass (more typical resolution) and having this issue, then that would raise some flags.
Have you done a test draw to see which head is running dry? You may find it is the same head and simply be a pump. Have they ever been changed, do they hold fluid in the capping station if you do a disway wash? Even if they do it may be something to dry, very cheap fix.
It is odd both your printers have the same issue, I would not point this at the rip though. Us, including hundreds (if not thousands) of other people use Onyx on their JV3.
I'm not sure how familiar you are to digital printing, you may be seeing Chromatic banding and mistaking it for ink starvation. Is the streaking you see alternating light and dark areas? One way to check is print unidirectional and see if your problem stops.