They will need to be replaced, a good English double gunsmith here in BC just did an overhaul of my H&H 12 bore, the job included machine, fit and heat treat 5 new screws ($250) and the engraving for 4 of the screws, with shipping to and from the engraver ($225). They look beautiful, and virtually identical to the originals. Money truly WELL spent (and I'm a very competent machinist...)!