I'm sorry, I don't have any useful knowledge here.I'm sorry about your Gosling.
I'm afraid I don't know much about Geese. I'll tag in @Goosebaby and @NatJ to see if they can offer suggestions.
Don't know if the answers to these questions will help them or not...
How is the ventilation in your brooder?
Any moldy spots within the hay/straw/or feed?
Tell us the temperature of the brooder on the warm and cold sides and what you are feeding. Do you provide grit?
I'm glad to see that someone else did have advice, but sad to see the update that the gosling died
