Oh man that is not good, I'm sorry to hear!!
I would use a two-part epoxy. Bad part is you will have to drain it and let it dry, then let the glue cure for 24 hours before refilling.
If that doesn't work ... I would call a place that sells kayaks, like Campers Village or Aquabatics, and ask how they would go about fixing a leak in a plastic (ie. not fibreglass) kayak - there has to be a way to fix those. See if they sell anything.
Good luck man !!
PS. Silicone might work too actually. Worth a shot anyhow.