What kind of seacocks are they? Gate valves or tapered valves? If they are bronze tapered valves they can be disassembled and you may be able to lap them back into shape. If there gate valve get them off the boat and put in a proper seacock. Silly to loose a boat for the price
of a few seacocks. And don't forget new hoses and quality clamps.
Tapered valves tend to get "wasp" shaped over time. Lap the valve in the body, clean it well, re-grease and re-assemble.
Mrs Joli lapping in 30 year old valves.