Y'all probably know this, but if u ever wanna clean your fretboard properly, without using steelwool (as was suggested to me by a local expert...:-\) then use lemon juice. Just a little bit on an earbud, rub rub rub, wipe it down quickly and voila!!
It evaporates pretty quick and the result is nice clean wood.
Now you know. 8)
On the left after lemon juice, on the right before.