Awww he's really super cute!
You know, I just realized something. Have you been checking his underside and the inside of his 'downside' wing to make sure he's not getting sores? There will be less air circulation there and sometimes it happens. Just a thought.
I'm so very pleased to hear one thing in particular: preening!
To me, with all the little birds that have come and go in my life, the one major benchmark I've noticed that spoke of true progress is preening. There's no need to preen if you're going to die, and preening - to me - is their signal of "OK let's get going on living now".
I'm thrilled!
Keep up the good work. I had a bird who was completely unable to use her legs and wings once. She was very small, a young pullet, and I fashioned a 'sling' for her out of a dust mask and a guineapig cage. The sling held her in a standing position with just enough slack to where she could put weight on her legs to gain strength, but when tired could just rest them and her hocks would be slightly bent. So she didn't have to push up much. She could reach food and water without moving. She had nutritional deficiencies from the first - hatched differently from the others, looked different. It took a long time for her to heal because back then NO one talked about deficiencies. It was "walk or cull". And I hadn't done all the reading up about them. And this was only about 8 years ago.
So I think with the knowledge you have at hand, hopefully you'll have addressed it sooner and the healing will take less time.
Please do keep updating us! Now there's a little face to go witht he "silky rooster" designation, so I know I for one will be watching for the updates.
Cheers!