GraphitALL guitar lubricant is a creamy graphite paste which stays in the nut slots well.

I also put some in the threads of my fine tuners on the Kahler bridge to keep them spinning unhindered. I highly recommend GraphitALL if you play a tremolo and use a graphite nut, an "after the nut" stringlock or locking tuners including Drop D types. $5.00 each bottle. Lasts years!