My umbrella has same issue since last September. Tried treating with injections, changed my handling of her and then had surgery. It did not hold. I clean her prolapse every day with a disinfectant I got from avian vet, but even with this she still gets dirty in vent area.
She shows absolutely no signs of distress. While it does appear she is straining to poop, it does all come out. Her eating and general disposition has not changed at all.
I did contact another avian vet and described the issues. She also agreed it is something very hard to treat. I'm debating whether to bring her to see the new avian vet. i just think I'm going to go through same thing (and its isn't cheap).
My original avian vet said he knows of an avian vet who does perform some other kind of surgery, but they are in FL (I am in NY).
Like you I am very perplexed about the situation.