My C-Max just got a little help from me.
To my knowledge I have never been asked about the cabin filter. At 237K miles it was filthy. But,.. I understand why no one wanted to mess with it. This was the most difficult cabin filter I have ever changed.
I also changed the wipers, engine air filter and plugs. Total time about 2 hours with the cabin filter eating up about 1 hour of the time.
I am hoping this will help get my mileage back up a little.