It has been said that Don Adams didn't do this episode because he said it was a reused plot from another episode/season. Im at a loss, was it ever documented what episode he was referring to?

This episode has the feeling of the MASH episode Temporary Duty where you see Hawkeye at the beginning (and I think at the end) and George Lindsay fills in for the rest of the episode.

According to TV.com, he thought is was a poor re-write of the "Schwartz's Island" episode from season 4.

http://www.tv.com/get-smart/ice-station-siegfried/episode/39867/summary.html?tag=ep_list;title;12