Is your crankshaft sensor clean and free from oil? The vacuum pump for the brake is known to leak oil and it will eventually drip down to the crankshaft sensor. Rebuilding the seal on the vacuum pump isn’t hard. I’m very surprised that you got a bad fuel pressure sensor.
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I have ordered a crankshaft sensor and will have a look after it arrives. It seems to be a slightly less accessible job than the top side sensors.

The fuel pressor sensor was soaked with petrol (gasoline) inside the electrical connection. It was not dripping, but clearly a seal was not doing its job. I'm not sure if that caused the 5V reading, but when I put the original back in, the fault code went away.

After that I replaced the cam shaft sensors (I do one job at a time, so if something fails, I don't conflate the two), and that seems to have done the trick.[/i]