Your leak is between hull and tube. Probably due to an object and vibration/stress that works up a leak over time. Mine was on, and at the ribbons, as they are slightly higher.
All zodiac leaks from one to the next chamber.
You have to get it off the hull. Deflate completely. Bend front down, two bolts appear, screw them out.
Hose the slot down with fresh water, to remove sand and obstacles. Apply a wild amount of washingup liquid. Tie the end of the hull down, and start pulling equally from both sides. It will fly right off.
Then buy a serous compressor, I used to manually pump mine. When done I was cherry red in my face, and thinking more on cold beers, than clearing my head and getting any serious work done. When you nail it, itís like you have just invited the freaking wheel all over again. Actually itís the most manly satisfying thing anyone can accomplish - better get right to it!