The marks on the face of the V2 nipple makes me believe they're "burn" marks or some kind of heat discoloration, possibly from when the d/s was cut down for when it became a belt-hanger for RotJ.
It surely isn't paint considering what its function was (something for another thing to sit on or over it---though at this stage, I don't believe there's any evidence to support the nipple was fitted into anything), and the motor is not powerful enough to cause enough friction between the nipple and whatever sat on top of it to make them; the marks also wouldn't be a near perfect line cutting across the surface.
I also brought this up in my research thread (at least, I think I did) but the collar/plug set-up for the antennae blades is first) the plug for the d/s-central rod to fit into to secure the blade to the hilt; and second) the collar on the outside is likely to keep the base of the blade from splitting. I had this happen on my V3 stunt when I was playing around with it to test some ideas, and wound up having to cut my blade shorter (for the better) after the base had split from the plug.