I ran a bunch of cases through my Dillon FL2000 tumbler this weekend. While I had the bowl empty, I noticed that a "skin" of some sort had formed inside the bowl. It didn't readily scrape off with a fingernail and felt sort of plastic like. I don't know if this is some sort of deterioration of the bowl material or a build up from media. I have only used corn cob with Dillon's polishing liquid in it.
Has anyone else seen this? Anything to worry about (like I need to look for another worry)?