He may be right but I doubt it, especially if you use a salt busting type chemical to clean the heat exchanger out, which is were I came unstuck.
I brought in the "professionals" to clean salt out of the seawater cooled water ways on the Yanmar and all seemed fine.
When I returned to the boat I even pulled the gearbox heat exchanger just to check and sure enough it was very clean.
About three weeks later during a four day passage it let go in the middle of the night and we had no drive.
At first, I thought I had caught a net and was confused when I went over the side to cut it free to find no marks on the hull and no net.
When I realized it was the gearbox I bypassed the heat exchanger and refilled he gearbox, it ran for about ten hours and then gave up.
The dinghy lashed alongside took me upwind for the next 75 miles.
An iron rule ever since on passage, is that the engine compartment is opened and a laser temperature gauge is used every two hours to check all the temperatures and also you will soon smell if anything is awry.
Seafever of Cuan