Hi BuffaloGhost,
thanks for that.
I did look at getting a new nut, but being a lefty, there isn't much choice, and what I found available didn't match the width of the original, so I wasn't confident of getting what I needed.
I have sanded down the nut, and placed ( not glued yet) to test and after 2 stages the sound is very nice and the action feels good. But the nut doesn't quite sit square in position yet, so I'm thinking about what to do, before removing any more material.