Thanks @BigPhil. After I sent my post I thought, of course I can't just switch the ECU to a different brand ECU. Although a bit fiddly, I got to the throttle body and I'm in luck with the one with a hole in.

Although quite a few poorly protected wires on the loom, so I can see why water ingress can cause a few faults!

Now to find a garage that can calibrate the TPS once the ECU arrives...