Thanks for the reply John, I've checked for oil contamination and the chain was replaced about a year ago.There,s not much mileage on this car 120,000 km but its been all stop start local runs from new.I just wondered had anyone replaced 02 sensors on this model with non OE ones and how did they get on?. On the other hand if whats going in is the same make and part number as whats coming out I can't see the problem,ie if the mercedes/bosch part number and the Factor/bosch part number are the same then they should be fine.Thanks for your help guys I,ll let you know the result.
Dominic.