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Parts 36, 50, 47, 49 are the water intake. Parts 35, 34 are a water bypass plate. If any are missing, simply replace them. Parts are the same as an Evinrude or Johnson 75hp manual shift, made for years.
On the other hand, maybe the guy doesn't know what he is talking about and the problem may be somewhere else. Most importantly, make sure the motor isn't burnt up from lack of cooling.