Once it had arrived, I managed to get a couple of inches of the tyre off the rim (not as hard a job as I'd feared) and poured in an old film containers worth of sealant which went into the tyre perfectly. It was when I went to pump it up again that it all went pear shaped... I was pumping as hard and fast as I could but a lot more of the tyre bead had come loose and there was latex vapour blowing out of parts of it and liquid latex spraying out of others so I had to think of a plan B. I took the whole thing apart and washed the latex off everything and ordered an Airshot tool and a couple of 50ml syringes off ebay (these are really cool as they come with a finer nozzle you can push on the end which is perfect for filling coreless Presta valves).
I removed the core from the Presta valve as recommended, pumped the Airshot to 140 PSI (surprisingly hard work even with a good track pump), connected it to the valve and let it rip. It almost worked but didn't quite seat the bead properly all the way around. I then went round the circumference of the rim and tyre with a cloth soaked in soapy water and tried again. This time it worked perfectly with the bead popping on all the way around. I then used the syringe to inject approx. 35ml of sealant into the tyre, screwed the valve core back in and pumped it to it's usual 80 psi. I then gave the wheel a good shake around and a spin and it's been holding air perfectly ever since.
