I had both my dogs sit just so I could check out their legs. Both do
ok. (Like the GSD sits) Both learned the "down" command from the "sit"
position ok, but Maggie was much slower catching on to the complete "down".
(she always wanted the treat before she got all the way down)

I don't think I would worry to much about the way Willy gets into the down
position, if he shows no pain otherwise. Dogs learn in different ways.