RE: horns
There is a big difference between a solid commercial laminate like G10/FR4 and a piece of ply with lightweight carbon (it's only 2 ounce stuff) on the outside surface. Structurally I have no doubts at all they are fine for the loads. However, with thin CF on the outside the bearing surface is narrow and under considerable point load at the edges. Bushed I would rate them fine. As is I am very dubious. And if these horns have a wooden core, be careful with the lube so you don't mush up the core and make things worse.
Even solid, there are differences between laminates, as in hand layups or cured under pressure and heat and sometimes partial vacuum as is often done industrially. I've had the opportunity to make some carbon/epoxy and glass/epoxy laminates before on an OEM vacuum laminating press, and with several tons of pressure on a 12"x24" sheet you get some pretty fine material in comparison. With a good tight layup and a cleanly drilled hole (high speed and a sharp cutter) I imagine they stay fine for a long time, perhaps as long as most aircraft do. But I don't think I'd use one without a bushing of some kind to improve the bearing surface anyway. G10 might be tough but glass/epoxy is also a nasty abrasive, essentially a 50/50 blend of sand and epoxy. Watching how fast it destroys HSS cutting tools can make you worry about these things.
MJD