Hi Jon, sorry for the delay.
Thanks for the insight on pulling ink through the system. Sounds like I'd have to remove the pressurization tube from the air pump, or fool the valve into opening while the system is off.
I'm pretty much resigned to rebuilding or replacing the ink assy on the 3880. However, a troubling issue is that the same thing has happened on my R2880 with VM. The entire channel will decide to quit printing. This happened twice this past weekend, after printing many prints without issue. It took PF injection and about 5 head cleans to get it back. Have you had complaints about any batches of VM? I have 2 bottles of batch 140508, purchased over a period of time. They both expire 2/2017 according to the label.
The 3880's dampers probably do need a refresh, as they're now 2 years old. However, since the same problem occurs on the 2880, I'm a bit worried that there is something else going on.
Thanks for all your support! It's this forum that keeps me a loyal customer