As a first step, I would only use the moisture from my breath and a soft cotton cloth to clean any fretboard (like cleaning your glasses).

And I would not use lemon oil. I would only use linseed oil in very small quantities. After application, continue to wipe off the excess every 15 min or so until you get it all.

Last, do not over do it. You can loosen your frets if you dump too much oil on the fretboard.

Peace

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