The cartridge faucet in my bathroom has developed a pretty steady dripping so I decided to give it a shot and replace it. I managed to remove the handle, but the screw ring that keeps the cartridge in place is stuck - I guess it's probably because of the limescale build up inside the faucet. (No limescale is visible on the top of the screw ring but I'm pretty sure it's the limescale). Is there any trick to loosen the screw ring a bit without having to remove the entire faucet and dipping it in limescale remover?
Try white vinegar. Drip it into the opening and let it sit for a while or soak a small cloth and leave it on top. Vinegar removes limescale from my flower pots and pet fountains.