Since quit's don't have a channel property, use $comchan using the nick, and N representing the Nth common channel.
i.e.
on *:QUIT: {
var %c = 1
while ($comchan($nick, %c)) {
var %chan = $ifmatch
/echo %chan This is a quit msg ( $+ $nick $+ ) $1-
}
}
Then use %chan, not $chan >:P