yea get high % of silver with flux in the stick. This will melt at a reasonable temp as opposed to copper 
 
If it is copper or brass 
 
Brazing Alloy 
Rod - Contents 15% Silver - 5% Phosphorus - 80% Copper - 
Brazing Range 1190 to 1480 F - Container Tube - Industry Standard-Good Near ...
 
Brazing Alloy 
Rod - Contents 7.2% Phosphorus - 92.8% Copper - 
Brazing Range 1310 to 1475 F - Container Tube - Copper to Copper or Brass Joints for ...
 
If it is aluminum repair these would be doable 
 
http://www.google.com/shopping/produ...w&ved=0CDgQrRI
 
You will need to watch the fins as they will be wanting to melt at brazing temps, possibly sink off the area with vice grip and wrap wet towles against the fin area on the end that is being repaired ........... 
 
 
 
Stop in any welding retailer with the unit and they will hook you up with the best stix for the job 
 
or simply replace unit with no muss no fuss as brazing aluminum is tricky