Never got anywhere with this apart from checking the wires on the loom up front were all connected. I bought a new sensor and was about to pop the wing off to fit it yesterday when I saw a wire hanging unconnected that I'd obviously missed. A repair I'd done before and it had slipped out from the rear of the connector.

A new connector crimped on and then heat shrink, I have an oil light again! Good, was making me paranoid..

Thanks for the help all!