The more traditional way to do something like this would be:

my $data;
do {
    #  Get web page
    my $response = $ua->post( $page, \%form );

    #  Check for errors
    if ($response->is_success) {
      $data = $response->content;
    } else {
      sleep 100;
    }
} until (defined($data));
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But I don't think that has much real advantage over your code or GrandFather's. Historical abuse of goto has caused a sort of disdain for anything resembling it, but in this case it's as clear as anything else.