Hi guys, i recently got the engine management light on my c200, had it checked out (not by mercedes) by a diagnostic machine and it says lambda sensor before cat needs replacing. but the guy told me he will clear the fault and drive it around for abit see what happens, so i did. after one day the light popped back up again. so we had a look at the lambda sensor which was absolutely covered in oil?! so he cleaned it out and cleared the fault again. a week gone by everything was good and i was loveing my car and bam! the light is back again. i havent had it checked yet but my gut feeling is the lambda sensor is covered in oil again... i dont know what to do, even if i replace the lambda sensor whats stopping the oil getting to it again? is this suppose to be covered in oil? i got my MOT in a week and its not gonna pass probably because of emmision, so i need to get this sorted. any ideas?? thx for any help