Yeah finecast is not a very successful material. I've painted a number of finecast minis now, and they often have big problems with air bubbles, miscasts and awful mold lines. It does seem like the miniatures have crisp, fine details though. But they're fragile and its ridiculously overpriced. Good luck fixing it!

Edit: Also worth noting games workshop has very good customer service and will likely replace defective models like yours. Give their customer service number a call. I bought a model kit with a large base that was warped out of shape, and they mailed me a free one no questions asked.