(1) The specification of performance left to a third party is effected by declaration to one of the contracting parties.
(2) Only the contracting parties are entitled to avoid the specification made for mistake, duress or deceit; the opponent is the other party. Avoidance must occur without undue delay after the opponent has obtained knowledge of the grounds for avoidance. Avoidance is excluded if 30 years have passed since the specification was made.