A couple of years later the ravages of UV rays had cause the C-10 to dry and crack—which was what Dicor had been accused of doing. There had been no leaks, but better safe than sorry. So I applied another coat of C-10. And repeated the process the next year.
When it was time to refresh the sealant again, a friend gave me a tube of Dicor. Oh, a comparison test. Science! Eh, same results.
A few months ago, another forum guy highly recommended 3M 4200 Marine Adhesive/Sealant. Superior UV resistance, he said. Okay.
Unlike self-leveling sealant, 3M 4200 is thick and gummy, so it’s harder to apply elegantly—especially when you’re on a ladder, stretching to the middle of the roof. But I used an old business card to spread the adhesive/sealant around and cover all the critical points. We’ll see how things are next year.