Yes, please continue the updates!
That all said, and with a complete read of this Thread, several things come to light.
You have been to Four (4) excellent CAV Clinics! They have provided an extensive battery of tests, including additional tests recommended by members of this Forum. So, with the possibility of PDD (possible carrier status?) no physical /medical reason can be found for the ailments your Parrot is presenting. Yes, there are limits to what the Avian Vet community can provide as there is with the Human side.
- I would 'Strongly Recommend' that you provide each of the Clinics that you have and are working with 'Written Permission' to communicate with each other and to provide /exchange clinical information with each other. Create a Team!
Whether you wish to admit it or not, there is a very strong emotional element functioning here!
- Rarely do Parrots kept or left at Sanctuaries for long periods of time not suffer emotionally. After all in their mind, they have been abandoned /have lost their beloved Human.
- The extensive change from a home to something a very long way from what could be even called a home.
- The Loneliness! The loss of their companion!
- Even in the best of Sanctuaries: miss-handling occurs.
- Even in the best of Sanctuaries: great variations in diet occurs, missed feedings and when fed, rarely is it defined for a specific Parrots.
To say that Emotional Behavioral base is not possible is likely you avoiding the reality of the error in placing your beloved Parrot in the Sanctuary. Parrots tie quickly and closely into our emotions and commonly react from that connection. Accept that you made a mistake and leave that emotion behind! It will not help you now, when you need to be the Adult providing comfort for your Parrot and not be lost in your mistake! It's in the past, leave it there. The vast majority of Humans feel this emotion! It is common!
- The behavior of your Parrot, IMHO, is consistent with that seen in rehomed Parrots and Parrots left for extended periods of time. Very common with the Amazons that come to our home. The Joy of Live has been lost and only time and assurance can slowly rebuild it back! This because, there is the near constant fear of again losing their re-found home.
- When not connected to a physical or medical driver, an emotional base is 'at present' the only other driver for Plucking. The reality is that plucking is a long time, on-going condition.
Keeping the skin from becoming dry has shown some success. We use a very fine misting product call Soother Topical Spray. It contains an active Aloe Vera distillate, with a antiprurtic and anti-inflammatory. Application should be limited to fine misting (not soaking) with use not greater than four times per day. Every other day (or when you commonly bathe your Parrot), extensive water misting (soaking) should occur to limit the build of the the Aloe Vera. This product is available at your Vet's Clinic or on-line.
Seek the support of your CAV to make minor changes to the upper Beak to create a slight smooth, round Beak end, in place of the point. Great care needs to be applied in not over rounding the Beak end. This commonly requires a re-treatment every 60 days. The blood spots are the result of the sharp Beak point!
Without a found underlining illness, the watery poop can be linked to the amount of water intake you report.
A vast amount of water intake is commonly linked to several specific aliments that your CAV's clearly know about and would very likely based their tests.
- It is not unheard of for Parrots to use their water bowls for daily baths, some only dipping their legs and /or beak multiple times though the day. Unless you are there every moment, it can be easily missed. I am not suggesting that this is what is happening, only that it does happen.
May this be of help!