Sailing from Bahia Algodones to Bahia San Padro, the starboard jib block failed. It’s nut suffered unseen crevice corrosion, causing the pin to pop out and the sheave to be slingshotted across the cockpit. The nut that failed was split in four places! Chloride ions can cause localized corrosive attack (pitting and crevice corrosion) of stainless steels.
Fortunately, the winds were light at the time , all of the parts were recovered, and a replacement nut was on-board.