Left joystick continues outputting forward or back motion after flick

I have an Xbox One 1708 controller. It's worked great over the years, and I've taken good care of it. It lives in a pouch in my laptop bag when I'm not using it. It may have been dropped once or twice, but I've never noticed any issues after those few incidents.

After some months of not playing rocket league (all I use the controller for) I recently got into it again and noticed after I flicked the left stick up or down (forward / backward), It would continue inputting movement in that direction as if it was pinned there. This is only the case for up/down movements, left/right movements are fine. If I move the stick in the opposite direction of the ghost movement, it will respond to my control again.

What do you guys think? Does it just need a good cleaning or am I due for some repairs / a new controller?