Does it stink? Vent gleet usually smells pretty bad.
If that's it, you can get a generic version of Monostat cream and after bathing their butts, dry them off and spread that all over the vent area. Put a dab of it in their mouth or on a small piece of bread or something they'll eat entirely too. I'd do that twice a day for a few days and it should be under control.
Also, probiotics helps a lot. Even if it's not vent gleet, it may help whatever that is. We have Hydro-Hen powder here for their water, but there are many brands of that. A small amount (tblsp) of of Greek yogurt twice a day has a lot too. I'd continue the probiotics for a couple of weeks to ensure their digestive flora is returned to normal.