Everyone is a beta tester for the next iteration of anything.
Anyway, I came to chime in about the 2-stop ND part from earlier. An ND filter with 2 stops of exposure reduction is called an ND 0.6 in the film world, and an ND4 in the broadcast world, and represents a transmittance amount of 25% light hitting the front lens element. The film (motion picture and stills) world calls it 0.6 because that is the optical density of the filter. The broadcast world says ND4 because, like gain, a stop is gained or lost whenever a value doubles or halves, so ND Zero or Clear is 0 stops reduced, ND2 is 1 stop, ND4 is 2, etc. The film world would be .3, .6, .9, 1.2, etc.
So, I've never heard of an ND4 or ND 0.6 referred to as an ND6. Maybe you speak "ND six" because we usually don't say a decimal (ie, "T two two" instead of "T two point two"), but it is always written "ND point six" or "ND zero point six". I would say "point six ND" or "let's reduce the stops by 2 with some ND" or something like that and the AC would know he needs a 0.6 ND filter. Never actually heard "ND6" before...but that doesn't mean it's necessarily wrong. A wooden clothespin might be called a bullet on one set and a C-47 on another. So long as the people who need to know whats-what on set do know and everything is communicated quickly and professionally, then it probably really doesn't matter.
Also, why say "cameras A and B" when you can say "Anabel and Beatrice"?
Back to the rainbow flare: that sucks. I would generally say it's the coatings of the lens being used, but if this is an internal problem...then I don't know what to tell you. The flare is actually sort of pretty...and I would chalk it up to a "character flaw" of the camera...which makes it more endearing. Of course, I prefer my piano to be slightly out of tune, and I use all kinds of filtration to soften the image coming into the camera on the day...so I'm not a big help. Forget I said anything.