ES13Raven
I also use crushed walnut.
I usually run several thousand 9MM or 40S&W brass thru it, in several different loads. Usually about 500-1000 pieces of brass at a time. The crushed walnut may last 3-5 times. When it is discolored (based on looking at new crushed walnut), I toss it.
I use new dryer sheets, as I don't use them in a dryer at all. I throw them away when they have picked up a lot of dust! usually about as long as the crushed walnut lasts.
And I don't use any additive, but I also don't care about shiny brass, just clean!
Hope this helps!