My guess that it was the neck card (CRT Amplifer card) causing the blue tube to have issues seems to be right. I swapped the green and blue neck cards tonight.
While re-adjusting the G2 for the green and blue, it was clear that the G2 control on the ‘bad’ neck card (now on green) was causing some random flashes on the green tube. The blue seems solid now.
Since the effect only appeared randomly, I watched a bit of a few different scenes to see if it would happen. I’m not certain it did, but it might have — the effect of ‘green’ flashing is different than that of blue — I seem to get ‘white-ish’ flashes instead of bright green. Could have been just the particular scenes.
I may just see how much a new neck card is going to run me from Curt. Alternatively, I could figure out the parts I need and order in new parts.
I snapped a few pictures of the neck card, and inside my projector. Take a peek at the gallery. I also added the CRT Amp swap instructions to the FAQ.