Actually for some series IMDB has a number for each episode, e.g.:
http://french.imdb.com/title/tt0534498/
http://french.imdb.com/title/tt0534549/
http://french.imdb.com/title/tt0534447/
so we could use that for very heavy series like "Chips" (could be done automatically, do not worry Stronghold, you won't have to move 300 cars :D)

The only problem is for cars seen in many episodes. But as you said we could list them in in each episode.