It may move okay but I have always found this method works;
1) Remove the screw and plastic pin from the clear plastic part
2) Remove the clear plastic part by easing it out the plastic grey finger out the iddle.
Give the clear part a thorough wash and/or wipe down, the groove where it slides is where the issue lies. Where the groove has an erected point is the part where the grey arm gets stuck. It would help to lubriucate that area and reassemble it to see if it works.