My rear wiper decided to stop working this winter and i'm just now getting around to fix it. the motor still works and drives the pinion gear but the wiper arm does nothing more than twitch up and down. I tried to remove the arm to see if it needs to be tightened. I can't get the arm off though. Does it need to come off? or can I fix the issue without taking the arm off? If so, how does it come off?