. "ier shall be forfeited unless it shall appear that the owner or other person in charge of the conveyance was a consenting party to or privy to a violation of this chapter; (2) no conveyance shall be forfeited by reason of any act or omission established by the owner of the conveyance to have been committed or omitted by any person other than the owner while the conveyance was unlawfully in the pos" . . . .