At least if you can aleviate his problem he'll be happier - bald or not. As for the petting, be patient. I have had my dear Timneh for 6 months now, and she is still unsure of my fingers. We work with her daily to try and train her to view fingers and sources of pleasure, not the strange things they must look like to birds. I imagine that our hands must be just too foreign to parrots, causing some of them to react fearfully.
Patience is key.
I always give my new birds a at least a month to warm up to their new environment before pushing tickles, etc. This, of course, will depend on the bird and its personal adaptablity - you kind of have to get to know them and learn to read them to know how comfortable they are. Good Luck and let me know what the vet says. Bitter spray are a cover-up and rarely work for long. They also threaten to bother the skin.