Brass radiator soldering advice

The flat side pieces on my 1915 tourer have separated from where they join the tank. I’d like to see solder them back, but don’t want to discolor the brass. They were like this when I purchased the car.

I would have an experienced solder guy do this job. You want to clean the parts very well first , which would involve grinding all the old solder off. Then use flux before soldering the parts back together. Finally it will be necessary to polish the brass until most of the solder is gone but leaving enough so that the joint will be strong. A difficult job even for an expert.