When I first got diagnosed I was given a soft case for my levmir and a harder case for my novarapid (nova pen 3).
I go out quite a lot and taking the softer case out with me has always been an issue as i have been so scared of breaking the pen, recently my case for my novarapid split
I think the case you are referring to is the grey coloured hard case..... mine split in two also! :roll:
Update to the NovoPen 4, its a far better pen and comes in soft case which is much firmer than previous soft cases. Just ask your gp surgery to alter your prescription to a NovoPen 4, or you could do as Catherine suggests and ring their customer care, can't see any problems with them sending you a replacement case free of charge.