How would you repair this?

[MikeK]

I'll probably catch hell for suggesting this, but I would use AWS Bag-23 Silver-Manganese brazing alloy. It is 85%Ag, 15%Mn.

Tight solidus/liquidus range starting about 1780F, very fluid at 1900F, it will easily wet and flow into the cracked section leaving a very small fillet. Much stronger than the steel when finished, and ductile enough to take some dolly work to make corrections after.

It contains NO copper, zinc, or cadmium, so the problems known to using standard yellow brazing alloys under paint are non-existent.