Custom Fields as Post Type Options

Your code…

function wpuf_update_vehicle_year( $post_id ) {
    $year = get_post_meta( $post_id, 'seek_property_year', true );

    update_post_meta( $post_id, 'seek_property_year', $year );
}

add_action( 'wpuf_add_post_after_insert', 'wpuf_update_vehicle_year' );

is probably executed, but nothing will change anyway because the thing it does is to grab meta data (with get_post_meta) for seek_property_year and then update the same meta data with the same value:

1. Get value for $post_id for seek_property_year. Lets say the value is 2010
2. Put value for $post_id for seek_property_year. Put 2010 into seek_property_year
3. …will result in no changes in database (nothing seems to happen)