Someone from PRS answered my question. He said, "Our SE nuts use a lubricated material based on the nuts used on our core U.S guitars."
I ordered the graphite tusq nut. I will try to install it myself.
I like my nuts lubricated with a good quality cream containing lanolin...... oh, wrong forum....
Guitars.... think guitars....
I'm feeling a bit inadequate because I couldn't hear any plastic kind of sound from my SE, however, the original nut did feel a bit soft and well, like a cheap piece of plastic. I ordered a PRS USA nut (as you would expect with... erm nuts, they come in pairs) Once the original nut was off the guitar I was able to compare it to the USA one. I did the drop test, the SE nut sounded a bit like... plastic, and the USA one had a distinct ring. I changed the bridge and the nut together.... my luthier lives a long way from me, about 6 thousand miles.... so it was more economical to do both at the same time (the price of the air tickets, arguing with the ground staff to let me take my guitar in the cabin...) Strumming the guitar, open strings, unplugged, it is much louder than it was.... handy if there is a power cut.... and this is where it gets a bit nerdy, if I put my ear to the nut (don't try this at home) I can hear it working.... the sound from the bridge of course much louder. So, in my opinion, the USA nut is more resonant, better at transferring vibrations, and vibrations are why we are all here.... I mean on this forum..... not the other one... well perhaps the other one too.....
There is most probably no real valid reason to go to these lengths, as someone said, the SE's are incredibly good guitars as they are, including the original nut. However, having said that, a guitar is the sum of 'all' it's parts, and only as good as it's weakest link!
Incidentally, my luthier was intrigued by the PRS USA nut, it has little sparkly bits in it..... I wonder what that is made from, does anyone know?