I would have thought if it's water damaged it's knackered and unreliable,so replacement is the only option.
I have seen the inside of the Ecu, there is about a 2cm square of a white residue on the board and one of the contacts was clearly burnt. I don't know what I am looking at but the auto electrician pointed that out and the main parts on the board. One of the companies I contacted said their cut off criteria is if the car was still starting in limp home mode, if that was still happening they can work with the Ecu it. Whether that would mean repair, replace parts or replace Ecu I don't know.