Paley Center has original broadcast of "The Thief"
http://www.paleycenter.org/collection/item/?q=Mr.+Belvedere+THIEF&f=all&c=all&advanced=1&p=1&item=T:48971
The reason I brought this up is because Edermike said in one of his posts that this episode might be edited on the season 3 DVD.
I haven't seen this copy yet, but I know that it is the original broadcast, because it includes an ABC News Brief on the swearing in of Chief Justice William Rehnquist, which did, in fact, happen on September 26, 1986.