I've found good information regarding the whereabouts of the Ferarri's but does anyone know what happened to the original full size GMC Jimmy the brown, gold orange one as well as the original Audi sedan?
Sold off after season 3 (old one(s)) and after the final wrap 1988. I was told once by somebody in california that he bought the Audi 5000 - but paperwork was not supplied back then so I am not 100% sure it was the real Robin 2 (this was claimed to be one the second ones, seasons 4-8).
Nope. As far as I am informed, it was sold off after season 3 (if I remember correctly) and to a local resident. After that the track was lost. TC's vanagon's resurfaced - one was offered to me some years ago but bought by a different collector in the end. The remainings of the other cars is a bit more vague (besides some good documented stories about the Ferraris of course)