Fixing slow drip from soldered copper joint

I installed a frost-free silcock about 8 months ago, including sweat soldering the silcock to the copper supply line.
Everything was fine until this week when I noticed a very slow dripping from the joint.
What is the best way to repair it? Can I just heat the joint and add more solder or do I need to take the joint apart, clean it, flux it, and re-solder?
Thanks
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rule is to take it apart,clean,add flux and solder.ive cheated a few times and just soldered it. lucas
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