HSSS,
It's simple if you are a good solderer.
The key is to position the part so gravity will flow the molten solder into the right place. Clean the part very well with wire brushes and sandpaper. Use acid core solder and a torch the correct size so you don't unsolder everything else.
If you want to get fancy, buy the silver solder packaged with a licquid flux at Home Depot. This stuff is expensive, but very easy to use for small jobs.
I have repaired lots of leaks in brass fittings and heater cores this way. Sometimes, it takes a second try but usually not. Good luck.
Paul