Truth be told, I don't like the lemon oil, or any of the other prepared fretboard dressing oils. Most of them are ineffective, and don't do a good job of replacing the natural oils in the wood.
The best stuff for the job is a couple of drops of olive oil (yes, swipe it from the cupboard) on a paper towel. Wipe it on, let it sit for a while, wipe it off. No, it doesn't get rancid. I've used the stuff since 1963, and it has always been the best. Don't leave it overnight, just a few minutes will last for a long, long time. Be sure to wipe off the excess with a clean paper towel, and you will be amazed at the improvement. I generally clean the fingerboard and polish the frets with 0000 steel wool first, wipe off any steel wool dust, then oil the board. Try it on your next string change, and you will never go back. DON'T do this on sealed boards like maple or Rickenbackers, only on the natural boards like rosewood, ebony, pao ferro, etc. You'll LOVE the results.