If you're cooking the stuffing separately, preheat the oven to 325 and butter a casserole dish.
In a pan, brown the sausage, breaking it into small pieces, until fully cooked. Drain the sausage and put it in a large bowl.
Add the stuffing, drained oysters, celery, beaten eggs, and onion, and mix until thoroughly combined. Mix in the croutons, oysters, celery, eggs, and onion until thoroughly combined.
In a bowl, mix together the reserved oyster liquid, chicken broth, and melted butter to make about two cups and pour over the dry ingredients, and carefully stir until combined.
If you're stuffing a bird, carefully spoon the stuffing into the cavity and proceed with cooking the bird. If you're cooking the stuffing separately, dump it into a buttered dish and cook for about 25 minutes until brown on top.