I have had good success using a 50/50 mixture of tung oil and mineral spirits. It soaks in good and does not leave a glossy finish. The antler is sealed against most stains but still has a natural look. Minwax wood hardener also soaks in fast but it is bit more glossy.
Try thin super glue.
I cut off a finger from a powder free vinyl glove and just put a dab of super glue on the handle and rub it on adding dabs of glue as needed. No need to buff. It does shine but a little rubbing with a white scotch-brite type pad takes care of that.
If you have a guard or butt cap, tape them and buff the edges after the glue sets. 3-4 light coats