New on here so any help would be greatly appreciated. I have an evinrude 25. Model number 25702H which comes up as a 1977. I want to replace my water pump impeller but when I look up the part I am supposed to have it does not match what is in the motor. I'm thinking someone replaced the lower unit with one of a different HP because my shaft does not match any that I can find for a 25. There is no keyway or pin of any sort. Instead, on my shaft, where the impeller sits the shaft has a hex head made into it. the top is round as is the bottom but it is a hex pattern at the impeller. The impeller itself has no metal insert in the middle, it is just all rubber. The hole is the same size as the shaft and it just slides up over the hex on the shaft to act as a key. Strange as it is, it works. Can anyone offer any clues as to what I have?