A water pump can be condemned without a defect in two ways. A good pump gets pulled because someone read a normal condition as a failure. Or a new pump goes onto an engine that kills it within months, and the part takes the blame. 

Start at the water pump weep hole. The shaft seal is designed to pass a film a few microns thick, and outside, that film dries into a crusty track. That's a seep, and it's normal. A leak is wet, glossy and still moving at cap pressure with the engine warm. Make the call warm, because a cold engine can show a wet weep hole that dries up once it reaches operating temperature. 

The second problem is harder to spot. Rust, casting sand, RTV beads and silicate dropout are all bigger than that film, and they cut the seal faces like lapping compound. 

This Motor Age Tech Tip brought to you by bproauto shows how to get both calls right.