cold. once you have removed the plastic cover you should see the screws that are holding the handle on.
once it is taken apart, examine all the parts carefully and figure out what is worn out or broken.
replace each washer, seal, or o-rings that needs replaced. be sure to only replace these items with the correct replacement parts. remember it only takes one little gap for the drip, drip, drip to continue.
inspect all the other parts for corrosion or other build up that may need to be cleaned off. be careful not to scratch or dent any of the metal because that could also cause a leak.
once you are confident that 