This car is PFL, early shape. I removed the bumper, and found the level sensor, as Al said, entering the (passenger) side of tank, blue connector. It came out easily. I checked in my spares heap and found the tank I saved off my Opel 2.5 MFL saloon, and the level sensor was at the back, as in RobG's picture. I took it out, same part and part no. as the failed sensor. I checked both with continuity meter and they both switched OK. The old float was a bit mossy, so I cleaned it. I tested it in water, and in less dense neat Opticlean, and floated in both. I conclude it was probably just in need of a clean, but anyway I put in the ex-Opel sensor.
The screenwash flow on this car is not so vigorous as my other Omegas. Is there a filter somewhere that I might clean, while bumper is off, to improve matters?
Thanks for all the help, Haynes seems unaware of the sensor.
Bumper off in 5 minutes, not this one. All went well until I pulled the bumper forward a bit, and found it restrained by by attachments both sides near the wing, only visible from below. N/s was a nut on a bracket, o/s was a cable tie. Haynes does not mention these.