The real question is whether it is still cleaning. These days I mostly use wet tumbling and stainless pins, but with the dry media I found that as the media clogged up with dust, the cleaning time stretched, and when it seems to be taking about twice as long (four hours instead of two), I could put a tablespoon of mineral spirits and a cloth rag or a piece cut from a Handi-wipe dampened with some mineral spirits and run it a couple of hours to get some of the grime out, and then it was rejuvenated for a little while. Next slowdown, I replaced it.