Sometimes leaking fuel will dissolve some of the engine crud/dirt and then not evaporate fully leaving a drip. However, looking at the cleanliness of your engine, I doubt there's much muck on it!

"Y mae dafad ddu ym mhob praidd"
1972 4/4, 1981 MGBGT, 1984 FLHT1340, 1980 XLH1000, 1990 ZX10