Some epoxy or JB weld will probably fill that crack. maybe find something that makes nice black ash or graphite and color it first?
I'm not sure it's appropriate, so discipline as needed, but I have an extra black horn button w/ yellow (can't spell the GM color ochre?) emblem if there's interest.
I can probably cobble together the bits to make the horn work as well if needed. That's sort of an interesting puzzle the first time
Please don't post here. PM me to keep the thread clean...