Part Number For 04 WRX Front Lambda/o2 Sensor
 

Need to change to front ( the one you can get at through the front drivers side wheel arch , pre-cat I think ) lambda or o2 sensor on my 04 wrx as my CEL has come on .
Does anyone know the part number , I've done a google search but I am getting 3 or 4 different part numbers , Subaru won't tell you the part number only the cost to fit one when you phone them .
Thanks in advance