Get some Naptha. It is safe to use on guitars, just don’t leave it sitting on the guitar. I prefer to remove the neck from the guitar when deep cleaning. IME it yields better results and is easier when the body is out of the way.
Wipe the Naptha on using a clean, soft cloth, work the neck with the cloth, then wipe dry and buff with a clean soft cloth. Repeat until the neck is clean to your satisfaction. This step will safely remove oil, grime, and dirt that has bonded to the outer layer of the finish.
After cleaning, if the neck is not satiny smooth; you can work it with some 0000 steel wool (do not use a coarser grain steel wool!). Do not perform this procedure on a neck that you have not cleaned. The steel wool could embed dirt and debris into the finish. If you have chosen not to remove the neck from the guitar you really, really, really need to cover your pickups with tape before using the steel wool!
- Rub the neck gently in the direction of the wood grain going in one direction only (i.e. do not rub “back and forth”). Work the entire neck with the steel wool making 4-5 passes. I like to work the neck in small areas until the entire neck has been rubbed. Do not spend a lot of time rubbing with steel wool, you are not trying to remove material.
- Using painters tape remove any debris from the neck using the tacky side of the tape
- Feel for spots that are still rough. Repeat steps 1&2 on each rough spot. You can repeat steps 1&2 an additional 2-3 times until the roughness is smoothed out.
If you have a small spot that is not responding to the steel wool after 3-4 passes with steel wool, you can take a wet towel and lay it over the spot then with a soldering iron on the lowest setting touch the towel with the soldering iron at the location of the roughness and move it in a small circle for one to two seconds then use steel wool to work the area as described above. You can repeat this several times, but be careful not to hold the heat too long and scorch the neck.
If you used steel wool on the neck, wipe the neck down with Naptha one last time then wipe dry and buff with a clean cloth.
Apply a guitar safe conditioning oil to the entire neck and side of the fretboard, let it sit for a couple of minutes, then wipe dry and buff with a clean soft cloth. I use Music Nomad F One oil. Even on a satin eurethane neck I do this for two reasons: First, your fretboard is unfinished and you will get Naptha on the side of the fretboard so you want to recondition it. Second, there could be exposed wood on the neck due to wear or damage to the finish and you want to recondition any wood that the Naptha may have come into contact with.