While I was replacing a CV shaft, I thought why not remove the trans pan and see what's up.
I always drop and drain, refill, then drop and drain every 12-15k miles, or once a year. This is the first time I have had the pan off, and I must say I am surprised by how clean everything is.
Barely any gray gunk or metal shavings were in the pan, even the magnets and screen were very clean compared to other vehicles I have serviced. I always use Valvoline/NAPA Dexron III ATF.
Have a look