Greetings My Dear New Best Friend Ed
Based on my limited experience making knives for fun (and no profit)
I agree with my good friend, coconspirator and hacksaw enabler Coffine:
It is most likely the horn.
I have had good results with sealing antler and horn with
Thin 2 part epoxy
Urathane varnish
Thin slowset superglue. The cheapest stuff is bestforthis.
Whichever you use, it stinks like you are going to be kicked out if you did it in the house.
Wear rubber gloves.
Maybe a respirator mask, If you?ve gotten sensitive to chemicals like me.
You want the grips to be slightly warm ... like 100 deg or so but not like in a hotbox.
Spread the goo with a disposable brush and try to get it to absorb.
If there is still some liquid on the surface after a few minutes, wipe it off, or you will have to file it flush later, which would really make you upset with me cuz the grips wont fit right anymore.
They still may need to be sanded for best fit.
Superglue spread over such a large surface is somewhat nasty, but is really good as a thin sealer,
And doesn,t seem to leave much that needs a lot of sanding.
Try it first on something else, wood fer instance, then step up to some scrap horn or antler.
That way you?ll get a feel for it before you mess up you expensive grips.
As always, your milage may vary.
Hope this helps
Prof marple