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( ‘….’ );.