Did it loose a valve seat ?
My heads were cracked by the seats, and the risk of
valve seat falling out is what led me to get new heads.
I am not exactly sure what gave up, but I know the exhaust valve is gone.
Also the water passages on the manifolds are VERY corroded. New manifolds too.
Saltwater boats Live and learn.
What heads did you do? Brad is suggesting Alum. heads.
I will be 99% freash water running and the extras sound worth it.