Go to a bicycle shop and get some slime.

Don't know how well it'll work for a
dinghy, but it works great on bicycle tires. WestMarine took over BoatUS's stores, so they may know a bit more about the
dinghy and if you can get parts for it.
__________________
Sailingdog
Telstar 28
New England
You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.
—Captain Malcolm Reynolds, Serenity (slightly edited)
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