I have a Cogswell & Harrison 450-400 2-3/8" BPE that has some missing finish in places on the buttstock and forend. Anyone have suggestions as to what to use to protect the bare spots and still keep the original finish?

Also, the buttplate is horn and it has some cracks forming along the edges and also some small holes in the buttplate surface. Some suggestions for restoring the buttplate would be useful, too. Thanks for any help.