87 90HP Mariner water pump help

[Kneeboardking]

I wondered if anyone has changed a water pump out on a 1987 90 Hp Maniner? I have owned this boat about 3 years and I was told the impeller needed to changed every year,Is this true? I don't have a manual, but the parts house is about 90 miles away(1 way)and he told me to bring the old pump/impeller with me to insure I recieve the right parts. My buddies say it's a simple process and if it needs to be done that often I need to do this myself. My buddies have changed them on different motors, but not a Maniner,is there anything special about his project? Cotter pin or speedo cable,does it need to be in gear? Help someone,We are going on vacation next weekend and now we are in rush mode to complete this project.

Thank You,
Kneeboardking