You could try some of that tyre slime. You inject it though the valve then inflate the tyre to normal pressure. It's supposed to seal almost any puncture present and future.
I've got a white and yellow one in bits tucked away in my mums shed
must dig them out as my little ones nearly 5 so a good age to see if she likes them or not
Lidl or Aldi sell it.I've had the slime on my ebay watch list since I found out about the leak I'll give it go.
Yep they do need to clear the shed and dig them out but as always they get bumped down the list of jobs lolIf not then you need get them ready for just before Xmas, they make stupid money then. I sold one for £400+ that wasn't anywhere near as good Faverruss's before he started polishing it