Why is my right thumbstick drifting out of position?

I’ve seen many questions about how to fix a joystick that is stuck in position, but that doesn’t apply to my controller. What happens is if I’m playing Call of Duty (or any game for that matter) I start to look upwards even when I am not making contact with the joystick. At first I thought that maybe it was getting stuck while pushed forwards, but then it started to happen for no reason. Then I decided to test something, I tested how far forward I would have to push the joystick to make me look up at that speed, then I waited for the joystick to malfunction, then I saw that my joystick was in the proper centred position: nowhere near how far forward it would have had to be if this was an issue of it being stuck/sticky. Does anyone know if I can fix this, or is this just a sign that it is time for a new controller?