I think I've tried almost everything that's come on the market in the past 50+ yrs, including some I've brewed myself. Recently I've been using WD-40 silicone spray: so far I haven't had any stuck(or difficult) cases. However, before the cases then go in the (wet) tumbler, I tightly seal them in a fruit jar after covering them with industrial acetone (inexpensive from HD), shake, shake, shake, and pour everything out through a metal strainer (disposing of the liquid properly, of course). After a minute, they're dry and not at all oily.