Radiator fitting snapped as I'm a twat

[Fazerider]

I've brazed aluminium with those zinc alloy rods and it's quite tricky. The ally starts to soften quite near to the melting point of the rod. If you're using one of those micro jet type burners with a tiny high temperature flame on thin metal it's easy to overheat and burn a hole through before you've got enough heat into the area to melt the rod. I've not tried with a hot air gun, but it may be that it would work better… plenty of heat, but not such a high temperature.
Practice on some empty beer cans first. and if that looks as if it's going the same way as the start of this sorry saga, take the rad to a specialist. :lol