With the guitar in playing position, hold the 13 fret with your little finger, right hand, and hold down the first fret with your left hand. ( I know you're right handed, I've seen the pictures of your guitars!
) Now tap the string (sorry, I should have pointed out Low 'E') aroung the 7th fret. There should be some 'bounce'. Only 1-2 mm. Assuming that there is some bounce, now try the 'D' string.
What's happening is, the string HAS to be straight and the bounce shows you how much neck relief there is.
The truss rod alteration is easy to do, but I have so many repairs in from people who have simply overdone it. As you look at the truss rod nut, be it at the headstock end or body end turn it to the left (as if you're unscrewing a screw) NO MORE THAN A QUARTER OF A TURN. Sometimes the change will be evident immediately, sometimes you may have to wait until tomorrow, but don't turn it again. If the guitar was fine before and this doesn't fix it, it isn't the problem.
Take a cigarette rolling paper and put it in the nut, under the problem string. You may have to fold it a couple of times to raise the string enough, but if this cures your buzz then the nut slot has simply worn away.
I hope that the truss rod adjustment works, because it's a far easier job than making a new nut. Hope this helps, let us all know.