There is only one cam adjuster but it's a big-ish job to replace. Best done by removing the inlet camshaft. I have seen a few unplugged & left with no obvious problems. I would agree with Andy & suspect oil is in the loom & travelled down to the 02 sensor.
Thanks for this Type49, I think I will leave the cam magnet unplugged for now as the motor is running smooth as silk, is that possible! I will keep an eye on the mpg though!! There is oil in the O.2 sensor & elswhere, but I have fitted MB's blocker line & a new magnet and have been washing all the plugs & sockets for a couple of months now. So it's fingers crossed that I caught it in time! Cheers. Owen.