Our experience was quite similar with Sam. When he arrived he seemed to be "calling his old flock", belting out loads of phrases, sounds, dog barks, and lots of naughty words. After about 6 weeks, he went silent, with the exception of whistles and the word "help". It's been over a year now, and our progress has been real slow. He mostly whistles, but has delighted us with the occasional word.
Have patience- it may take a while for Wozzie to begin to say new words, but when he does, it'll be such a treat!