I never use the slow cooker or dutch oven or roast pan with out spraying it FIRST with spray oil. No scrubbing necessary to clean it, no liners needed, and it works well to prevent foods sticking to the pans. I use the cheapest spray oil I can find.
All the suggestions have been great, and I think they just might work if you want to take the time to do them. I think I would replace the crock itself and forget about cleaning it.