How can I repair a hairline crack on the rim of a toilet pan?

I bought a Roca Sydney Pergamon toilet on the 15/8/00, it has developed a hairline crack at the rim on which the seat rests and the crack is slowly getting longer. What can I do to repair it ? I have inquired of Roca as to a replacement under there guarantee but Roca will not replace the toilet free of charge as they did not guarantee their sanitary ware untill 2008 but I can buy one from them for £235:00p inc.vat. I do not want to do this if I can reair the crack.