Grohe faucets like similar makes, have a cartridge in the handle to operate hot and cold water functions. This cartridge has two valves with rubber seals to prevent leakage inside of a sealed plastic cylinder. When the seals break down, leaks start in your faucet. The design of the cartridge in Grohe faucets makes it fairly simple for any homeowner to replace them, and basically refurbish their faucet. It takes about half an hour to finish this task.
Turn the water to the faucet off by closing both hot and cold water valves underneath the sink.
Remove the screw in the handle of the Grohe faucet. It is located on the side of the handle near the base. Use an Allen wrench to take out this screw, called a set screw. Slide the handle off.
Grasp and turn the cap sleeve (located under the handle) to the left to loosen and remove this part. Employ the use of large pliers if required. Then remove any adaptors or temperature control parts by loosening their screws with a screwdriver and taking them off.
Loosen the two screws in the top of the cartridge with the screwdriver and take the cartridge out of the faucet by gripping the top stem with your fingers and pulling it out.
Install a new cartridge in the old one's place. Install both cartridge screws. Replace adaptors or temperature control parts removed previously in reverse order now.
Attach the cap cover and tighten it by hand. Reinstall the handle by pushing it onto the stem and turning the set screw to the right to tighten.