Tom, how many miles are on your C280? I have two W202, one with 171K ('95) and the other with 62K ('98). Given mine are 4 bangers, there is a difference, but with everything I have read it would lead me to believe that it is a head gasket problem. That's exactly why I stayed away from the 6 cyclinder versus. Check the underside of the oil filler cap, if it looks like 'butterscotch' or specically it does not look like oil - then it is probably the head gasket. I know you stated it has not used any coolant, but I just had our ML head gasket done and it hardly used any fluid, but the underside of the oil cap was 'butterscotch'.