Title says it already.
I have a problem with the controller, anytime I wanted to make a circle, it will straight draw a line at one of the sides like this:

Joystick.png

I have opened the previous controller, try to find the problem, and I found out that the joystick itself is the problem. I took of that little plastic thing, and now it was able to make a full circle, however, I never knew how to fix it, so I wanted to put it back together, but I broke a lot, so I got a new one for christmas.
I lost the receipt, of course, and I want to try it again, this time with help from you guys.
Is there anything I can do about it?