piston damaged in 140hp Suzuki 1997

[glenbudden]

I have a 140hp Suzuki motor (1997). After hearing an unusual knocking noise in the motor I took it to our local repairer to get it checked. (It was only serviced 1 month ago). He has informed me that the top piston is damaged due to saltwater. The water was also evident in the other 3 pistons. Apparentley all of the seals/gaskets are OK and the only explanation I have been given is that the water must have entered the exhaust port when I took a wave over the back of the boat. This seems very odd to me. Has anyone ever heard of this happening or have they got any other explanation?