Re: replace water pump ( How often ? )
With a newly acquired used motor, you don't know how strong it pees with a new impeller. Lot of folks say 2 years I go 3 years or 4. Probably a lot of 10, 15-year-old impellers still in service - but it's not too much effort considering the potential consequences. But it is too much effort, considering the cost of parts, to *not* replace it regardless of condition, once you open 'er up for inspection. Just my opinion of course.
If the housing is scored *at all*, do the full pump kit.