😬 As no one seems to have answered your original question -
As far as I am aware it is a Caterham part. I'm not aware it can be obtained elsewhere. It seems most problems result from water ingress, so if you do buy a new one, you can prolong it's life by sealing the gap around the electrical terminal using silicon. You can also mount the sender remotely, higher up behind the radiator and out of the way of the spray and muck. To do this, use braided hose and appropriate connectors. Again, Think Automotive can supply.