Hi, I encountered the very same problem, the API has been updated very recently (today?).
You now have to add "access_type=offline" while building the https://accounts.google.com/o/oauth2/auth
call to get the refresh token.
I noticed another change, but not an incompatible one: the name in the Authorization header while making a call. It used to be "OAuth" but now it's "Bearer".
Both names work as far as I tested.