A while back I did a little study on fretboard treatments.
Mineral oil leaves a residue that eventually becomes sticky and attracts dirt. It sits on top of the wood. It will soften the top layer of the wood a little, which isn't necessarily a good thing on a fingerboard that deals with hard fingernails, metal string friction, etc. I've seen woods, including fingerboards, treated with mineral oil that you could sink a fingernail into. In fact, my wife used to treat our maple cutting board with it, and you could literally write your name in it with the edge of a finger. So be careful with that stuff.
Lemon oil is essentially naphtha with a little lemon scent so it doesn't smell like the dry cleaners (naphtha is the main ingredient in a lot of dry cleaning stuff). Lemon oil is good for cleaning the fretboard,
and should be wiped off immediately.
Bore oil is for woodwind instruments that pick up spit and moisture from the instrument being blown into. The wood on such an instrument would rot unless it was treated with something that adhered to the outside of the wood and left a residue of oil. So its purpose is far different from the needs of a fingerboard, that gets moisture and oils at the same time from your hands, but isn't in a confined space like the inside of a blow hole, and it is open to the air for quicker evaporation, leaving the oils from your fingers behind. In many cases, woodwind instruments are also finished with a coating inside.
If you've ever looked inside a clarinet case, you'll see one of those disgusting looking cleaning sticks with cloth attached to it to dry the danged instrument after playing it. They need those. The things get sopping wet with smelly spit. And they need that oily goop on the inside of the clarinet to keep it from rotting outright from their breath and saliva. No wonder clarinet players can't get dates. Their cases are full of smelly goo.
But you're a guitar player. OK, maybe you have a harmonica, but they're so cheap no one cares if it rots. In fact, people will be happy if your harmonica rots, because then they don't have to listen to it.
There seem to be several schools of thought on fingerboards. Some people think that an oily fingerboard will somehow look better, or last longer. I can't speak to looks, but it sure won't last longer. I have a 1965 Gibson SG Special with a perfectly fine fingerboard that has never been oiled in its lifetime. Ever. And it has sat through neglect, Michigan winters, dry heated rooms, my kids' rooms, dorm rooms, winters in the equipment van, you name it. Not atypical, by the way.
How many cracked fretboards have you seen (where the cracks were from lack of oil)? I've never seen one. I've seen some broken ones from being dropped. I've got friends and session guys who come in with very old guitars to my studio, some dating back to the 30s, and none have a cracked fingerboard. And they don't baby them with anything.
I have never oiled a maple or ebony board. I had a tech who once nearly ruined my rosewood Artist II fingerboard, by gooping lemon oil on it and leaving it sit for hours, but other than a little swelling by the frets that eventually went down, all it did was discolor and aesthetically ruin the maple inlays. I could have killed him for doing me this "favor". It could have loosened the glue holding the inlays, but I was lucky.
I've used only lemon oil stuff to clean rosewood boards, immediately wiping it off as recommended by PRS. PRS' recommendation is a pretty good one. I haven't needed to use furniture polish on the fingerboard, but I tried it on a rosewood neck and it made it slick without any goopy buildup.
I'm of the school of thought that fingerboards are made with oily woods that generally don't need treatment of any kind. They need an occasional cleaning and that's it. A wipe down after play if your hands are sweaty (mine are very dry).
I believe that people love their guitars, and want to be good to them, and so buy products that somehow are touted to do good things, but they are usually doing more harm than good.
How often do you see a guitar with polishing swirl marks that wouldn't be there if only the owner had simply used a soft damp cloth to clean it and dried it with a microfiber or chamois? It's not like a car that sits outside and needs an occasional wax to keep the road grime and bird poop from abrading the finish!
But that's me. I'm a minimalist.
However, if you ask anyone who's worked on my guitars, or have seen them, they'll tell you that regardless of how long I've had them, they're in amazing shape. Except that old beater '65. But its fingerboard is in amazing shape. LOL!
