I think the big problem with a dirty cabin filter in the W210 is that it makes the blower or fan motor work really hard and does not let it slow down. That has caused a lot of motor failures. All air pushed by the blower goes through the filter -- it is drawn through the filter by the motor. I changed my filter after I bought my '98 e300, and the filter looked like it had never been changed. I now change the filter every year or two and the motor runs lower speeds.