Trim the fat
You don't need to add oil to a slow cooker, the contents won't catch as long as there's enough moisture in there. You don't need a lot of fat on your meat either. Normally when you fry meat, a lot of the fat drains away, this won't happen in a slow cooker so trim it off, otherwise you might find you have pools of oil in your stew. This will give you a healthier result and it'll still be tasty.
bbcgoodfood.com/howto/guide/10-top-tips-using-slow-cooker
You don't need to add oil to a slow cooker, the contents won't catch as long as there's enough moisture in there. You don't need a lot of fat on your meat either. Normally when you fry meat, a lot of the fat drains away, this won't happen in a slow cooker so trim it off, otherwise you might find you have pools of oil in your stew. This will give you a healthier result and it'll still be tasty.
bbcgoodfood.com/howto/guide/10-top-tips-using-slow-cooker