For the last month one of my adult female radixes has had this reoccurring problem with a crusty vent. Last night when I checked on her I was shocked to see what appeared to be an abscess on her tail. Pushing on it I thought I would lose her from something like this. I felt the best way to help would be to open the area up and get some sulfadiazine on it.
To my surprise it wasn't an abscess but a retained shed problem. She had retained an entire shed and when she defecates some of the feces has gotten trapped under he old tail shed and caused an irritation(something like diaper rash).
She spent about an hour in a shed box but it didn't do any good so it was to the bathroom sink for a manual shed. After the shed was complete she went into a container with a cloth for substrate. I'll keep her in this for a few days and watch for improvement.
This photo is from last night. The white stuff isn't infection but sulfadiazine. This morning much of the redness is gone and it looks better. I'm guessing she'll make a full recovery. She is one of my rescued females from last year. She has taken to Ranch life very well and is a joy to interact with.