2. If you want to preserve the CTE and charset, you should use `C-u 3 e'.

   Unfortunately, this seems to be broken for text/plain messages.  The
   buffer-local variable `gnus-article-mime-handles' is not set for
   text/plain.  I don't know if it's omitted on purpose -- does someone
   know?.

   If it isn't supposed to be set, then here's a patch that will make
   Gnus construct a MIME handle, when you do `C-u 3 e'.