[flatheadmurre]

If you are going to solder it...rivets has to come out to be able clean both sides.
Stainless wirebrush !! any leftovers from sandpapers or other abrasive will work against you.
Solder water(flux) in bottle and a brush.
Low temp solder made for radiators...if you try using hightemp for plumbing there is a fair chance you melt another place and create more leaks.
Rose bud tip in an Oxy/Acethylene torch.