Hi! This is my first post on the forum.
I don't own a grey but saw one in a pet shop who seemed sick and who, as the title says, was eating only sunflower. I talked with their owners who are in fact a vet clinic (where I used to take some of my sick birds) who own a pet shop across the street from their headquarters. The bird is kept in the main space of the pet shop, in a big enough cage but under constant strong artificial light (from room illuminators), in draft (customers entering continuously) and noise (same customers talking to the shopgirl). His droppings are light green (not toward yellow, but like you would mix green and white painting colors) and viscuous, like some diarheea, a homogenous paste of uniform color, not mucoid.
They told me they tried to make him eat something else but he doesn't touch anything but sunflower. The bird cannot be handfed or manipulated in any way as bites anybody and has an extremely strong beak, really dangerous. If someone aspproaches him he also start screaming, sort of agressive yeld, very loud and impressive but scaring the customers. The owners apparently were not puting at least calcium, vitamins in water, neither probiotics or acv. I typed, printed and handed them a four pages text about grey diet and fat liver disease, translated from the websites dealing with this domain / subject. They seemed reticent to receive advices, probably because they arte vets (but have no experience with birds).
I feel pity for that poor bird and want to help him, even in the conditions the owners are not cooperative. If I could receive some practical advice from you, I can go and handle them another text and they may want to follow the advices.
I know how useful would been some photos with the bird and especially with the droppings. Unfortunately, I was not inspired to take some photos when I was there and I'm afraid would not be prudent to do this now, as this may cool the relationship with the owners even more, making them even more reticent.
I have no experience with parrots but I'm rescuing pigeons for more than three years, I keep over thirty at my home and know to a certain degree their problems, how to hand feed etc, so I will understand your indications and find easy to put them in practice, if I can convince the owners to let me do this.