Thank you, as always. What concerns me is these guitars have been in the desert for a year, 5% humidity, and many days when the temperature varies 60 degrees in one day, altho I keep them in my bedroom, which is of course, the most elementally safe place. But still. And now I've got fret sprouts. After a year.
One day, Jesus said to his disciples, "The kingdom of heaven is like 3x^2+8x-9."
Thomas was confused and asked Peter, "What does the teacher mean?"
Peter replied: "Don't worry. It's just another of his parabolas."
Lemon oil or boiled linseed oil are both fine. Look to see if there are other ingredients. If there are, look further. Neither oil is for cleaning the fingerboard. They are to keep it from drying out. Oiling the fingerboard might be OK once a year, but you don't want oil gunking up the surface. Your fingerboard is most likely not thirsty. Oil finishes can last for decades, For cleaning, the same as the rest of the guitar. Soft, damp cloth. Fingerboards build up gunk faster than the rest of the guitar. For deep cleaning I use 0000 steel wool. Followed by a damp cloth to remove the dust and residue.
On a finished fingerboard, like Fender's maple fingerboards, treat it like the rest of the guitar. It has the same finish so the same care is appropriate.
Anyway, this is my opinion. I believe many people use too many "products" on their guitars. Your mileage may vary.