Mercedes has us changing the engine air filter every 40K miles. It seems high. The last time I checked, it was quite black. How often do you change?

 

The owner's manual for my older MB says to change the air filter(s) every 50,000 miles.

I pull the filters and check them every 25K miles, or so. If they're super dirty, change them. If not, blow them out with a leaf blower and put them back in.

 

I think 40K miles is reasonable, but ...

I do the same. I check mine every 20K miles. If they look OK, I do blow them out with the air compressor and reinstall them.