Here is what I've tried.
I've edited /etc/ssh/sshd_config on the remote AIX system
X11Forwarding yes
X11DisplayOffset 10
X11UseLocalhost yes
as well as set $DISPLAY
DISPLAY=localhost:10.0
export DISPLAY
...reboot
connect via RHEL
ssh -X me@hostname
run xclock
xclock
get the following output:
X11 connection rejected because of wrong authentication.
X connection to localhost:10.0 broken (explicit kill or server shutdown)
also xauth list
doesn't print anything.