Here's the fingerboard extension and the main part of the crack. I spread it open so I could get glue into it.
The crack runs from the end you see here up to about the 6th fret. It's not that deep the whole length - it gets much shallower and tighter after about the 14th fret.
You can see the glue squeeze-out into the fret slots. I cleaned that up by carefully running a razor saw through the slots.
Then I sprinkled the sawdust on the crack and worked it in my hand, brushed off the excess, and then put some thin CA on the dust.
I used the famous Frank Ford method of filling these. Take an X-acto (with a new blade) and cut into the divots lengthwise to make some raised wood fibers.
Unlike the crack fill, I used a small ruler as a lever to try and really pack the filler in.
Then again brush off the excess, but leave a small 'hump' of it on the divot.
Looks like loose leaf tea, doesn't it?
Let the CA dry - if you need to, add more filler or CA. Next step will be to file the fill down close to the level of the fingerboard, and then sand the whole board.
The Complete Martin Guitar Restoration Saga
Repairing heel break
DIY chisel for bridge plate removal
DIY bridge plate removal iron, Pt.1
DIY bridge plate removal iron, Pt.2
Steam removal of bridge plate
Bridge plate removed
Tongue brace removal
Crack repair and brace scallop
New bridge plate Pt. 1
New bridge plate Pt. 2
Patching hole in top
Final fitting of top patch
Installing carbon fiber rod
Fingerboard crack repair, Pt. 1 (This page)
Fingerboard crack repair, Pt. 2
DIY fret bender tool
Refretting Pt. 1
Refretting Pt. 2
Tuner shaft repair
Neck reset - dovetail fitting
Measuring neck set with DIY jig
Gluing the neck with hide glue
Fitting bridge pins
Making bone saddle
Making a buffalo horn nut