Macbook bottom case cracking

My Macbook is cracking around the power input, on the bottom left of the case and the mike. The cracks have been developing over the last year. I've taken it in but they've refused to fix it, claiming it is not an 'identified problem'. It's now got to the stage where the power input is starting to push out. I suspect it's the plastic reacting to the heat. I'd be keen to hear if anyone else has experienced this particular problem. I suspect that, far from being an unidentified problem it's probably pretty common.