Remember that 2 traits will come to your help every now and then: Patience; and Perseverance.
Sometimes there's just no cure to plucking, some birds pluck out of habit, however, that has no negative impact on the bird's ability to talk and amuse you as well as most of the times the bird has no health issues--physical or mental.
So be patient and try to win his trust which is not that hard, don't expect one step a day approach, even if it is an inch of progress you should and will be proud of it.
It's a slooooowww, steady, but rewarding process.
Good luck
