or perhaps it is just the ISO adapter?

The Mk1 didn't have an ISO adaptor, just this bundle of cables from the dock:

Looking at the pictures, it definitly looks like it's been in and out of the sled only a few times at most. Definitly not enough to show wear and tear from car use. Expecially since the Mk1 sleds didn't have the cuts around the points that made contact with the players case.