You can use old solder, but fresh one is always better.
If you spot cold solder joints or cracked with magnifying glass, than you simply can re-touch the old one .
try to go http://www.parts-express.com/cat/desoldering-tools/520 and choose 45W desoldering iron.
If you spot cold solder joints or cracked with magnifying glass, than you simply can re-touch the old one .
try to go http://www.parts-express.com/cat/desoldering-tools/520 and choose 45W desoldering iron.