MacBook Pro screen has a strange oily looking spot
I recently bought a MacBook Pro laptop sometime in April. I'm not sure exactly what model it is, but it has the Thunderbolt port and a backlit keyboard. It is a thirteen inch screen. I recently noticed something strange - The laptop was developing an odd spot in the middle of the screen, similar to what you might see when you press your finger on it. After a couple days, I noticed that it had spread, and there was now an oily looking spot, as if there was oil on the screen, but it was behind the display. It's not as noticeable when the screen is lit up, but it stands out like a sore thumb when the screen is off. I can't think of anything that would have caused this except that I recently repaired the screen at iResQ, and I also carry it back and forth to school with me every day. When it is in my backpack, it is inside a plastic hard shelled outer case and a soft carrying case. I'm not sure what caused this, but any help in fixing it would be greatly appreciated!
tl;dr MBP screen has weird oily spot/pressure marks.
MacBook Pro, Mac OS X (10.6.8)