Right, I had a steady CEL for a week and the garage tells me I need a new Lambda sensor, part no. 22641AA042 and it'll cost me £313!!!!
Anyone got one I can have cheap?

 

The same age Impreza will fit, do a search for 'cheap lambda' on the web, you can usually find them starting at about £85 all wired up and ready to go, less if your happy to swap your connector onto the new sensor.

Simon