Well… I’ll add my experience. First, I do use butyl as much as possible, but found chainplates a difficult application. The main problem we’re the cover plates are welded to the chainplate. This makes it difficult to get a significant amount of butyl in place still allowing the mounting bolts to pass through the bulkheads. I ended up using Sikaflex 291. Second, check your deck core. If you’ve had a drip, your core is wet. Replace and protect. Last, inspect the chainplate! I am not an expert, but would love to hear from one. I had one chainplate with substantial crevice corrosion. I understand it is related to moisture getting trapped without enough airflow to dry it out. If you’ve had a drip, I suspect the moisture has spent some time seeping through the failed sealant. I have not dye tested the old chainplate, but would like to. The exterior visual was enough for me to have a new one fabricated.
Just my experience… Mike Rose s/v Shannon Rose C&C 39, hull #23 Sent from my iPhone