Water is the number one enemy of destroying pcb's---especially when there is no conformal coating and
any type of salt involved. SMD and sided boards are even worse. Corrosion on the on Eyelets is another problem.
Short of removing every component/connector and washing the entire board which is impractical, you are asking for trouble.
Even if you do get it going, it would be a matter of time before something else will quit.
No doubt, your efforts in small business are commendable but your time would be a lot more profitable repairing non water damaged boards----(I used to have a (non marine) repair business---saw many many water damaged cameras).
Most often, due to corrosive nature of salt, there is conduction in-between points and no telling of eyelets etc... visual inspection is the only tool.
Telltales are definitely there.
Good luck.