i don't use a slow-cooker, but it takes a long time for the marrow to widge its way out of the bones in my stockpot. it's fine to just push it out and add it to the broth. or just melt it into scrambled eggs.
most cw recipes suggest defatting the broth once it's chilled. i save it along with the broth and use bits of it each time i use the broth. adds mouthfeel and flavor and is a good way to get pure animal fat.
As I ate the oysters with their strong taste of the sea and their faint metallic taste that the cold white wine washed away, leaving only the sea taste and the succulent texture, and as I drank their cold liquid from each shell and washed it down with the crisp taste of the wine, I lost the empty feeling and began to be happy and to make plans.
– Ernest Hemingway