rewrite for subpage seems to loose parameter

That’s because in the URL https://mydomain.cl/vehiculos/vehiculo/1599 there are no query parameters, and no GET parameters.

This is because you rewrote them into the URL, and they are now query variables. For the same reason $_GET['pagename'] wouldn’t work, neither will $_GET['auto-id'].

Instead, use get_query_var( '....' );.