Originally Posted by grumpus

That would be fine if epoxy had the right tensile properties, but it doesn't which is why it's only used to glue the structural fibres together. My plan would be to remove the damaged section by sanding it until there are no cracks remaining; this should leave the stay in two pieces with a gap in the middle and feathered edges. Then epoxy a pre-made carbon tube inside (you'll first need to scrub inside the tube ends with a gun brush and acetone to remove any release agent) and layer carbon over the outside to restore the original dimensions.