Update:

I found that the Brass nut I installed on my LP Studio seemed to be causing the strings to bind in the string slots, so I re-shaped the back of the nut after lightly tapping it free from the PVA glue (very glad I used the PVA glue rather than 2-part epoxy), anyway, after re-shaping the back of the Brass nut to hopefully reduce the string-binding, I glued the nut back into place and re-strung the guitar, it didn't seem to make much difference, so I'm going to try replacing the Brass nut with a Bone one that I've ordered from Stewmac, unfortunately they are out of stock but Stewmac will send it to me once they have some in stock, I've actually ordered two of them and the string-spacing is standard Gibson spec which is a bit wider than the string spacing on the Brass nut.