It looks like the glue has failed also Kev.
What i do, is drill out the soft pith from the antler, right to the boney outer edge. I use electric insulating tape, and put some around the antler to keep the glue off. Mix some epoxy,- i find araldite best, and spread a thin layer of epoxy around the inside of the boney edge, and the rest of the araldite that i had mixed, i mix with horn filings or saw dust to a paste, and pack that into the hole. You can now either let that set , or you could push a wood dowel into it, and let it set fully. When set, drill into the center about 3 inches to take