From your description of the break and the pic, does it run from the bottom of the headstock to the side and the first tuning peg, then from the first tuning peg to the second one but from the inside to the outside of the head,
If it is running between the shafts (dowels) of the tuning pegs then it may be a case of the holes needing to be "eased" a little, being that the shafts may be a little to big for the holes causing pressure and the break.
If this is the case then I would remove the row of machine heads, open the break without causing it to split anymore, fill the crack with wood glue (preferably Titebond original) although a good wood glue should suffice, clamp the repair, leave for 24 hours.
When you have done that push the shafts through the holes to see how easilly or difficult they go through. It should be a snug fit so that they don't move about or bind as they go through. If there is any binding a light sanding of the holes to relieve the binding should do the trick.
It's worth waiting to see what Setch has to say on this as well before you go any further unless it is apparent that what I said is the problem