hi i hope you don't mind me changing it a little.

#seen_nick on
on !*:JOIN:#: {
  hadd -m seen_nick $wildsite $+($remtok($hget(seen_nick,$wildsite),$nick,32),$chr(32),$nick)
  if ($numtok($hget(seen_nick,$wildsite),32) > 1) {
    echo $chan $timestamp -- $nick used these nicks earlier: $remtok($hget(seen_nick,$wildsite),$nick,32)
  }
}
on !*:NICK: { hadd -m seen_nick $wildsite $+($remtok($hget(seen_nick,$wildsite),$newnick,32),$chr(32),$newnick) }
alias -l saveseen_nick { .hsave seen_nick $qt($scriptdirseen_nick.hsh) }
alias -l loadseen_nick { 
  if (!$hget(seen_nick)) { .hmake seen_nick 10000 }
  elseif ($exists($scriptdirseen_nick.hsh)) { .hload seen_nick $qt($scriptdirseen_nick.hsh) } 
}
on *:disconnect:{ $saveseen_nick } 
on *:exit:{ $saveseen_nick }
on *:start:{ $loadseen_nick }
on *:connect:{ $loadseen_nick }
#seen_nick end
menu nicklist {
  -
  .Turn Seen Nick $iif($group(#seen_nick) = On,Off,On): $iif($group(#seen_nick) = On,.disable,.enable) #seen_nick | echo -a $timestamp -- Seen Nick is $group(#seen_nick)
  . $iif($numtok($hget(seen_nick,$address($$1,2)),32) <= 1,$style(2)) Check $$1's Previous Nicks: echo -a $timestamp -- $$1 used these nicks: $remtok($hget(seen_nick,$address($$1,2)),$1,32)
  . $iif($numtok($hget(seen_nick,$address($$1,2)),32) <= 1,$style(2)) Delete $$1's Previous Nicks: echo -a $timestamp -- $$1's Previous Nicks Are Now Deleted. | hdel seen_nick $address($$1,2)
  -
}

Edit: added the nick event.