Short answer: Sugru!
I was recently on holiday, swimming every day, when I noticed the internals of my Pebble Time were fogging up, which meant just one thing: the water resistance had obviously failed. I immediately took the watch off and started thinking about how I was going to repair this.
When I returned home, I pried the top of the Pebble Time off and looked at what was sealing the watch – it appeared to be some sort of rubbery self adhesive strip. I looked around the internet and thought about what I could use, but then I settled.
I cleaned off all of the adhesive rubber, and then carefully cleaned the internals of the watch, removing dust and fingerprints from the glass, before rolling out some Sugru to a very thin diameter – as close to 1mm as possible – and then laying it out around the lip on the inside of the pebble time plastic chassis.
Pressing the glass down firmly and securing it with clothes-line pegs, I then carefully trimmed off the excess Sugru that squashed out.
Leaving it overnight to cure, I tested it by going swimming the next day and, I'm happy to say, it's back to it's old water-resistant self!