from my experience if it is leaking on the seam you will not be able to stop the leak.
Prolly have to replace tube.
if the tube repair kit doesn't work, and it is a small leak try the following;
get some Q-bond (can get from most decent hardware store).
take a piece of normal plastic like from a checkers packet and cut into a small square approx. 2cm square.
pump up the tube
pour some Q-bond onto the piece of plastic (2 or 3 drops) that you have cut and press down over the leaking area of the seam, obviously with the q-bond between the tube and the plastic.....saw a dude put his finger into the glue once and he had a major prob after 5 mins....
when you do this try and get the Q-bond to go between the 2 pieces of material that make up the seam.
press down firmly for about 2-3 mins.
once the glue has hardened you can peel the checkers plastic off and the q-bond has hopefully pushed into the cavity between the seam.
I used to have a duck, and whenever I got a hook through the tube I used to do this, and 2-3 years later the glue was still holding.
good luck....
