I have the same problem, still waiting to hear back. however
You can contact www.bristan.com as bristan look after the damixa products which are all part of Masco group (all quite confusing) or check out the bristan website. you will need to know the exact model and make. The new valve is nearly as expensive as the tap itself so you might not have much joy there, best of luck anyway.
Conor in Ireland, March 2010