I have one hen that is prone to vent gleet. We live in a place that has valley fever. Sometimes chickens from other parts of the country have not built up any immunity to valley fever(It is a mold that is in the soil) and so they have problems with it. I had an australorp that did not get sour crop but had a fungal plug just before the lungs--she died of pneumonia--UCD gives us a free necropsy services so I sent her in and that was the result. She was 10 months old.Never seen a case of vent gleet, though had to deal with quite a bit of sour crop. Most of the crop issues have been when it quit functioning as a symptom of a system-wide shutdown, not specifically a crop problem, though. Gotta keep them out of the compost pile where they can get hold of moldy feed.
In young chickens with sour crop and then vent gleet, it is treated with monistat 7.