My fuel tap gasket has failed. I followed this useful thread to identify that the tap is Suzuki part 44300 05112 renumbered 05115. I may have missed something obvious but I have not however been able to see a part number for the gasket. From Discount Motor Spares I sent for gasket 44341 28070 which looked to be the thing, but it turns out to be a tad smaller, marked 23 (whereas my old one is marker 25) and is ribbed on both sides (whereas my old one ribbed on one side but flat on the other).
Any help as to where I can find the necessary gasket (sort of the ultimate solution which is to buy the whole tap, which is available) would be much appreciated.