I don't think pencil lead would do any damage. The trick might be to produce some graphite dust to apply to the slots rather than trying to force it in with the pencil tip. It could look messy with white bone nuts though.
If steel doesn't score it then why would a pencil. A pencil is what we used way back before all these packaged guitar care kits came about.
Besides, it's fun going into your music store and telling them "I need some nut sauce". The clerk told me they get this several times each day.
Get a bottle of powdered graphite. Store it in a small zip lock bag and keep it in your guitar case. Use as required, but only a very small amount is needed. You don't need to fill up the slot with graphite.
I found a silicone goop, same but not packaged for guitars. Twas like a quarter the price. Not to be cheap.
I use powdered graphite. It came in a plastic syringe dispenser. I don't remember where I bought it, but I just push a very small amount into each nut slot, and then blow the excess away before I string the guitar and tune it up.
I used a pencil, but it left graphite dust on the headstock, so I moved to nut sauce. Works fine, and doesn't make as much of a mess.
The powdered graphite can be found at any hardware store that has a lock and keys section. I got mine at Lowe's. Cost was negligible - couple bucks or so.
+1 on Big Bends Nut Sauce. One of their larger syringes will last you many many years. Been using it for over a decade with results as-advertised, especially on Tuneomatic bridge saddle slots.
Big Bends Nut Sauce works very well and does not leave a stain or residue . I think it comes in 2 sizes , with a needle like syringe tip for pin point accurate usage . Really good stuff !
Not sure about that. If you are correct, then for sure, avoid it. I guess it does matter "how bad" and how much, etc. I'd challenge anyone to put a generous portion of Vaseline on their body paint and leave it for a year. Something to look into though.
I use pencils but my method is to scrape the graphite of the pencil on the corner of the nut so the dust just falls into the string slot. I wouldn't use the pencil tip against the slot itself, although like said above, if the string in there doesn't damage it a pencil shouldn't either.
