I had my original chain plates dye penetrant tested at 12 years old. The stainless fabricator in NZ showed me a tiny red line and said see that. He then proceeded to bend 3/8" SS with his bare hands. it was crevice corroded about 90% through.

304 stainless is highly vulnerable to crevice corrosion. 316 less so. It usually occurs where you don't see it - oxygen prevents it. Under the caulk where water gets in from the chainplate moving under strain is where it happens most.

I replaced all my chain plates with 316 in 1997. Ten years later, back in NZ I had the same guy test the replacements - they were good. 316L is supposed to be even better.