Here's what I put in RELAY route block:
$var(rr) = t_relay();
xlog("L_NOTICE","SLD: in RELAY, t_relay returned $var(rr)\n");
if (!$var(rr)) {
sl_reply_error();
}
In 4.0.3, t_relay gives a -1 in the case that there is a physical network issue (in my test I have a "-j DROP" iptables rule)