Tru Oil on a fretboard?

What type of fretboard?
Dark woods don't need finish.
On fretless same. Depends on what you're looking for, on fretless, there will be a massive change of tone with and without finish.

 

I was reffering to fingerboard on fretless. They will get change in tone.

 

Never tried it. We don't have that here in Serbia.
The thing on fretless bass is to have enough light touch with left hand just to the point where you get buzz. This will make sure your fretboard lasts.
My friend is a luthier and made some amazing basses, their fretboard (wenge) lastet about 7-8 years and then started to get worn.
I prefer no finish on fingerboard of fretless bass, and prefer dark woods.
And again, there is no finish required on fretted bass with dark woods. But maple and similar woods do require one. But I'm not sure which one. Hope this will be helpful

 

I use Fret Doctor exclusively on my rosewood and ebony boards. It is designed to penetrate and stabilize the wood. i learned about it years ago on the Les Paul Forum.

Bore Oil for the Fife and Fret Doctor