Every shroud and stay ends at a chainplate: a stainless or bronze strap that comes up through the deck and bolts to the hull or a bulkhead below. The whole rig's load goes through a handful of them.
Their weak spot is the deck slot. When the sealant there fails, water sits against the stainless in a tight, airless gap, which is where stainless steel corrodes worst. The damage is out of sight, below the deck and inside the bolt holes.
What a surveyor checks
Each chainplate at deck level for rust weeping and failed sealant, then below deck with a light and a magnifier for cracks and elongated bolt holes. The structure it's bolted to, for movement and lifted tabbing. Records of when they were last pulled. Surveyor Wayne Canning advises pulling them every 5 years once a boat is over 10 years old, and a surveyor recommends removal and dye testing when the visible signs justify it.
In the report
"Starboard cap shroud chainplate, rust weeping at the deck slot, sealant failed. Visible section below deck sound. Remove and dye test before offshore use." See chainplate crevice corrosion.