If you are brazing you add a lot of extra heat this will melt all the soldering that holds the item together.
With brazing you are using brass rods and a flux, the item you are brazing has to be cherry red to obtain the correct temperature to melt the brass and effect the repair, if you do this you will melt all the solder that holds the radiator together.
If you cannot undertake the repair yourself wit solder take it to a radiator repair facility.
Do not braze use solder.