I fixed one similar to the way Paul did.  I used Accra Glas Gel.  I had a fairly large syringe, no needle.  I know what caused mine, overtightening the front triggerguard screw.  Someone had removed enough wood around the receiver ring that the front screw would bottom out in its hole.  I took a bit off the end of the screw and heard the crack as I tightened it down.  The crack ran all the way in to the trigger slot, as I had to clean some epoxy out of that area after pumping it in.  I imagine it will be good for another 100+ yrs.