Probably the wrong thread to ask the question mate, but yeah, you could probably solder the float where it's leaking, but inside the float, where water has been trapped for a long time, it's probably pretty pock-marked with little craters of corrosion, so it'll probably "hole" somewhere else soon.
That's what happened to the brass float on my riding mower, and because it was pretty old I didn't think I'd score a new float, so I soldered it, and soldered it, until the weight of the solder was 'probably' causing the float to sink into the gas, and it kept flooding. Good thing with our bikes, is that you can buy new parts for them, so you did the right thing by buying a new one. Cheers, Terry.