Elmers Craft Bond Tacky Glue
I'm suspecting it's about 5 years old, I think it's been here since we bought the house.
Prep? Ha. Throw a blob of glue on the broken edge of the pad, squeeze it together, and try to clean the excess. If necessary, scrape some hardened glue with razor blade.
Wait for it to cure, and you're good to go. Let's see how long it lasts though.