Repairing 3" heat exchanger on M-50 diesel

[PhantomBoatwork]

I am just finishing up a complete rebuild of my M-50 Universal diesel and I took the trouble to sandblast the outer shell of the 3" heat exchanger. I noticed a very small crack near one of the fittings in the brazing joint. I was wondering if anyone has had experiencing in rebrazing any of the joints on a copper/brass heat exchanger. I am a medical gas plumber and have had some considerable experience in brazing copper tubing and fittings, but I'd rather not find out my limitations on this. Any help out there?

[NCboatrx]

Solder will be safer here.
Stanley