<VV> One Low-Beam Out... Sometimes

[Michael Mauro]

Re: my 67 coupe... with low-beams selected, right-side low-beam is out; when I press the floor switch for high-beam, all four beams illuminate. Question... do I need to replace the right-side low beam; or, is there a wiring issue? (Of course, if the fix is a new bulb, I'll replace both to insure the same amount of illumination). Please advise. Thinks! 
Mike Mauro