If the impeller is 40 years old, it should be replaced no matter how good it looks. After sitting for that long, it will only be a matter of time before it falls apart and you probably wont notice the motor overheating because of it.
These three horse motors have the water outlet incorporated into the idle relief port on the front of the exhaust housing and it is covered by a small plate. It’s hard to see the water coming out as it can be a spray or a dribble. The best thing to do would be to replace the impeller as part of a preventive maintenance program and invest in a cheap infrared thermometer. The IRT can be used to scan the running motor while the lower cover is removed. 
