To make a long story a little shorter, he ultimately decided to disassemble the printer down to the point where he could remove the damper assembly. This printer is much like the 3800/3880 with the stationery carts. So, on top of the actual head sits a damper assembly which receives the ink, through tubing, and directs it down to the head. After removing the damper he used a syringe to gently squirt ink into the VM port of the head; he had slipped a folded paper towel under the head and the VM ink flowed through without any evidence of being blocked. (He subsequently reassembled the printer and it shows no improvement.) So, now he's thinking the problem must be the damper for that port.
Unfortunately, there is very little information to be found on the function of the dampers. He has the impression (from reading any references he could find) that the dampers are extremely delicate and contain a very, very fine screen. So now we're trying to figure out how to approach dealing with the VM damper. If he removes the tubing from the damper assembly (the tubing is attached as a unit of all colors, and appears to have to be removed as a unit, exposing all channels to air) he's concerned that he will have to do a very expensive "ink charge" when it goes back together.
To possibly avoid the charging issue (but if it has to be, then it will be done) we're thinking of attempting to inject ink or cleaning solution backward through the exposed bottom of the VM damper port to dislodge/dissolve the blockage. He's quite concerned, however, that we could damage the damper by applying too much pressure. Before he continues, we're looking for all the help we can get. And, in the far recesses of our minds we're wondering if the problem could even be an electronic issue, meaning perhaps the VM damper is not receiving an electrical signal directing it to fire.
So, has anyone here attempted to deal with a damper issue? All ideas welcome. Thanks for taking the time to read this.