Keep up the B complex And watch the feet to make sure they stay as good as they are now. You can see how the gosling does without splinting hopefully he/she won't need the splints anymore
If you can post a video it would be good if we can see how well the gosling is walking.
Sounds like great...
The water needs to be warm so they don't chill. Being they are only covered in down they can't maintain their body heat to keep them warm. I'd try the tub start with the water up to tops of their legs. Then as they start enjoying that raise the level of the water. until they can float you have...
Call and ask they may not carry Durvet but if you look at that link there are other brands.
I don't have a TSC close by so I ordered online this is the brand I have. Agri labs. The Durvet is another option. it says injectable but we use it orally.
Durvet Liquid B Complex usually TSC carries it, it will say injectable but we give it orally over a small tasty treat so we can be sure they get full dose which is 1 ml
here is info.https://www.backyardchickens.com/threads/niacin-deficiency-in-waterfowl.1367557/
as for his feet any type of...
Have you been placing his feet on the shoes like we rec this has to be done while they are still very young? and are you giving the gosling/s Liquid B Complex which is the best thing for leg weakenss which is niacin def.
Poor little one. I'd try making a boot use a plastic container and cut the container to fit the bottom of the gosling's feet, wrap in vet wrap [coban] to protect from sharp edges. Then lay the feet out on this boot and use vet wrap to attach to the goslings feet go up around the ankle to make...