My Xbox controller's left analog stick is unresponsive in only the right direction.

I've had this controller (Which is a PDP model that is listed as being officially licensed by Xbox) for about six months now. Very suddenly it has begun to experience an issue where the left analog stick is unresponsive when I move it right. I am unsure if it is due to a sensor problem or just something getting in the way under the casing. I had attempted to open the casing and check myself but fear causing more damage by trying to look.

If someone could give me their opinion on the problem, and whether or not I should buy a new one, that would be extremely helpful.

:)