This photo is horrible, but I believe you are referring to the area that secures the pocket castings..
The hole at the end of the rail, is where the casting inserts. The counterbored hole on the top side is where the pocket casting screw is inserted.. Correct?
You can remove the broken wood, replace it with new wood, and re-tool it to match the existing profile.
Otherwise, you can use a JB Weld epoxy putty to rebuild the broken area. You may still need to re-tool the area. If you do a decent job forming it, you may be able to get away just with using a file and basic hand tools.