Pump looks and feels ok. The saying ( if it's not broke, don't fix it) would that apply?? The boat was last tagged in 2003.
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Since there is no motor in front of it, pull it, throw a thrust bearing in it, new grease seals, new packing, inspect it for excessive wear and throw it back in. The half a day now can easily turn into a couple of days once she runs.
It ain't broke because it hasn't been asked to do anything...

JMHO
GT