There are a couple of members of this community who've had plucking cheekies.

sivholm's greencheek began plucking after a move:
http://community.livejournal.com/parrot_lovers/1821771.html

missbehavann's Ouija plucked his chest for non-medical reasons, also:
http://community.livejournal.com/parrot_lovers/2861340.html

In both cases, the feather-picking didn't last. Greencheeks are pretty temperamentally straightforward, compared to most pet parrots. I'm sure that whatever's causing this behavior, whether psychological or physiological, is nothing you and Gavin can't overcome.

I'm glad he's seeing Rupiper. By far my favorite vet, ever. :> Keep us posted.