Saw a guy in Boise skip the chimney cap inspection entirely, said it was 'just a hat'. That's a fast track to a water damage call. | Chimney Sweeps - Opinions Matter
My buddy's place in Denver had a cap that looked fine, but the flashing was totally shot. They found out after a heavy spring rain when the ceiling in his living room started dripping. Cost him like four grand to fix the drywall and rafters.
Yeah, that's the worst kind of leak, the one you don't see. My old apartment had a similar thing with the bathroom fan vent. Looked totally normal from the roof, but the seal had failed under the shingles. Took out a chunk of the bathroom ceiling after a solid week of drizzle.