Fix shower controller for my mom

My mom lives in Korea and I visit her once every two years from Canada. This time when I visited her, she was struggling with the shower temperature controller. It was not moving at all like something was stuck inside. I quickly realized that the cartridge inside of the temperature controller got stuck and not moving because it’s been too old. I removed the cap, sprayed wd40 and cleaned with toothbrush. After doing it for few times and rearranged the controller, it was fixed like new. My mom was so happy that she can now enjoy ‘not too hot’ water bath.