No auto mount in gnome-shell Arch linux

I'm outlining this esoteric problem for the 1 in 1*10^6 Google search that gets here and perhaps this is a solution for somebody.

The problem: Arch Linux, GNOME 3, with SLIM login manager.. external USB won't auto-mount, returning the "Not Authorized" message. KDE works ok, just not GNOME shell.

After checking I was in the correct device groups, eg. "storage" for the USB device, I fiddled a while with policy kit. None of this worked, and the recommended forum solution is to add ck-launch-session preceding the gnome-session call in xinitrc, but this didn't work either.

It turned out for me the solution was to add dbus-launch to my xinitrc:

.xinitrc:

exec ck-launch-session dbus-launch gnome-session