Well, rechecking your earths can't hurt. I would also be tempted to check the high beam switch at the handle bar.
Main thing is 0..2 -0.4 volts difference isn't goint to damage your battery. If I was checking it myself I would be putting my oscilloscope on it and look for AC noise on the DC but as I've only ever hear of regulators failing open or closed or balast resitors failinging open, none of which would give you your symptoms, I still think you are fairly safe.
Go on...get out and ride it
I'm off to Scotland on mine next week Hope the sun comes back out!