I didn’t think it would work, but good ol’ cyanoacrylate (aka Super Glue, Krazy Glue) bonded my torn master cylinder dust boot. There’s one little 2-3 mm slit that’s not quite airtight, but it’s as good as it needs to be. I had to stretch it over the top of the piston to install it, and I am confident the bond is at least a strong as the rubber.
