Sad story and I wonder whether we will get something like £300 if we get into an accident. For sure you would not sell the car for £300 if it was working but then if you are in a accident, there is a very good chance that the insurance will only pay that much and then you will have to figure out what bicycle to buy to replace the 6.
If your sensor is bought new from a shop, maybe you could return it and get a refund. If you bought online, maybe you will have to pay the postage, but still it should be a straight forward refund. You just say that you tried it and there is no difference, so you would like to return it. In the past I had received an oil filter for the old car from Car Parts 4 Less which of course came in a Euro Car Parts box. It was one of these filters that do not have the metallic cover, it is just the paper filter that you fit in a plastic attached to the engine. Somebody had opened it and tried to do something with it. This did not stop them sending it to me. I contacted them and I got a replacement but you may have a chance to return it to the shop like that guy returned the oil filter. It is still crazy that a sensor goes for £90 and the whole car for £300.