We "recommend" changing the engine air filter every year or 12,000 miles.
But then we are greedy. Though depending on how dusty the area you live the more you should replace it. The air filter does effect your gas mileage.
We usually recommend trans service after 50,000 miles.
I have replaced two transmissions in the past few weeks, both on MLs. One was due to a leak, it was 2.5 quarts low and burned up, and the guy next to me also just did one on a ML.
Most transmissions don't need a fluid flush, most leak out of the electrical connector. Replace the connector and fill it back up, flush done
The one weak point of the 722.6