LAST EDITED ON Nov-28-11 AT 02:43PM (MST)[p]Sounds like the core has dried on you.
If they were mine, I would drill a 1/16th hole into the back of each horn (to let the moisture into the core and release the sheaths), submerge for 2 days, then repeat the sweat process. They should pop off with ease after this.
Once off, clean then borax the inside of the horn sheaths then allow to comepletely dry, clean the skull either via beetles or boiling (I prefer beetles), then afix your horns back onto the horn cores after you have the skull cleaned and whitened to your preference.
As for the tiny holes in the sheaths, a tiny amount of sculpt-all with a tad of texture and coloring will fix it in less than 5 minutes. No one will ever see it. This will be done after the horns have been re-attached to the skull.
Whatever you do, DO NOT BOIL THE SKULL WITH THE HORNS ATTACHED!! It will stain the horns forever.
I hope this helps.
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DRSS