When it comes to customer service from Games Workshop, I have always received second to none great service. It just happens that a Warpsmith (chaos space marine) a good friend of mine received, had some issues, primarily with the power axe the model comes with. The model itself was fine and usable, but the axe was literally missing a large chunk of the handle beneath its hands.
I suggested that he give customer service a call, simply to see if they could replace the axe, or replace the model. So he did.
Customer service was very polite and straight forward, and asked for the numbers on the package. They then said they had been having problems with that batch, and they promptly within a couple days had a new Warpsmith delivered straight to his door step.
I had heard some people say that Games Workshop had stopped replacing whole models, or that they would require him to return his damaged Warpsmith, but that was not the case.
The second model was perfect. Once again Games Workshop comes through. Bad finecast model and your simply sitting around bitching.... just give them a call.