So, today I was back home with my cleaning kit. Took the printer apart, pulled off the dampers and injected PF into the head. That seemed to do the trick, although I haven't printed anything yet. The nozzle check looks ok now though, so fingers crossed. While I was at it, I did a complete cleaning of the capping station, wiper and platen. It was dirty, but not bad.
For completion, I've answered your questions below. Let me know if you think of anything that may have brought this about. Thanks!
When is the last time you agitated the cartridges?
> The printer was under a friend's care for about a month. They probably didn't agitate, but used it repeatedly with no issues.
Have you run the VM out of ink in the past?
> No. When I looked at the ink lines and dampers, they were full.
What is the actual ink level in the cartridge in comparison to the Status monitor reading?
> 3880 carts don't have accurate ink monitoring. I try not to let them fall below half.
Did the printer sit unused for any amount of time before this large print job?
> No, they had been using it for a while before I got there. It was working fine for about 3 hours that night, then had issues with various colors, finally settling on VM as stated above.
How old is the printer?
> It was bought refurbished about 1.5 years ago.
Have you performed a thorough cleaning of the print head, wiper blade and Capping station?
> See above