Thanks Kathy, I poked it with a sterilized needle but air doesn't come out. Just a gooey clear fluid so I don't think it's the ruptured air sac. Does that sound like anything you've encountered?
I have him away from the other ducks while he's got the goo on him. I don't want them to get him dirtier than he has to be
That I haven't seen. Any chance you could take him to a vet?
-Kathy