it's common in gliders? I thought that was very rare.
If it had not been a vet, I would have wondered if it might be possible your glider is a boy who had pom off neutering, that could leave a small slit where a girl glider's pouch would be.
Glad you are able to get her/him to a vet in time. Sorry, I'm not up to date with gender neutral pronouns
but how is everything going now? Any more updates?