I have never changed the water pump on my 03 50hp mercury outboard and am thinking about changing it. It is still pumping water it's just not as strong a stream at idle or low rpm. Should I get just the pump or a kit with the gaskets and o-rings? The motor has been in fresh and salt water but every time I came home from the coast I would always stop by a lake and flush everything real good. I always flushed the motor every day it was in saltwater.