I have a small 6 horse Mercury motor with very limited usage but it is 20+ years old. The water pump is working as water is being discharged but with the age of the motor I am considering replacing the pump as a preventive step. I have owned many motors over the years and have never had a pump fail but I have read people, mainly service shops recommend replacing every 5 years.I am wondering if you would suggest replacing it now. I am also wondering if it will fail gradually.