Not really...
I've successfully soldered them, using an old-fashioned soldering iron - the type that takes forever to heat. Once heated, though, that thermal mass becomes an advantage. The trick is getting the solder to flow-out properly, without causing damage to the float. I find that fairly easy & straightforward but, for the sake of disclosure, know that I've had decades to learn many types of soldering. That said, this kind of brass repair is easy. The area to be repaired must be cleaned; a shot of solvent, scouring with steel wool or scotchbrite, followed by another shot of solvent, will get the metal clean enough. 60/40 acid core solder is self-fluxing and the alloy melts at a low temp ~390F. Lead-free solder won't work for this. Bring the soldering tip up-to-temp, testing it with solder; when it melts & flows onto the tip, you're ready to begin. Heat the area to be repaired, give it a few seconds, then touch the solder to the float and the soldering tip. You need to heat the part enough to melt the solder. However, molten solder in liquid form, improves heat flow dramatically and you can use that to get a properly-flowed-out solder joint. Apply just enough solder to cover the break, then sweep the soldering tip over the area moving just slowly enough to get a smooth, mirror-like bead. Then remove the soldering heat. That's about all there is to this type of repair. Float cracks tend to be tiny, rarely larger than a pinhole in total area. You want to work slowly enough to get the solder flowed-out (meaning that it actually bonds to the brass, sealing the leak), then quickly remove the heat before anything can be affected by it.
If you lack any soldering experience, at all, this may not be the DIY repair for you. OTOH, if you have even modest experience, it's easier than it might come across as being. Seriously, this is very similar to the kind a slot car fab work I learned...before starting high school.
