Ipod video 30GB Model A1136

I just purchased an ipod from my friend. He kept it in his car's glove compartment. .The plastic must've swelled a bit and when it cooled down it left these hairline gaps of clearness that contrast greatly with the black finish especially when the screen is lit. It's inside the plastic, not on the surface, like when a car window starts to crack and it slowly spreads as time goes by. I think it was from enduring the heat from the summer. Can the case be changed? Where can I get it done? How much will that cost?