Don't know if you've solved this or not Tony but an interesting little circuit. The only three points I see that would only effect both low beams are the dimmer switch, the point at which the low beam wire connects to the dimmer switch and what looks like a connector in the low beam wire after the grommet. Have you tried just rapidly toggling the low beam dimmer switch when this happens? I thought it interesting that the right lamps are back fed to provide 6 volts to both headlights for DRL's. Pretty crafty and cheap to do.