Cannot run X over ssh

I _can_ and always have run X stuff over ssh on my 11.2 installation.

I maintain a machine remotely for a friend, have brought it from 11.3
to 11.4 remotely long ago.
At some point in the early days of 11.4 I _did_ run also X stuff there.

Otherwise the machine is just fine but now I just can't do X anymore.
I don't know for how long cos it's rare to need to.

I hadn't done this at home for a long time either so I started testing.

Same result, no can do. Not on _any_ 11.4 or above.
I get these messages:

All 64 bit machines (11.4, 11.4 Tumbleweed and 12.1):

$ssh -X
$ xclock
connect /tmp/.X11-unix/X0: No such file or directory
connect /tmp/.X11-unix/X0: No such file or directory
connect /tmp/.X11-unix/X0: No such file or directory
connect /tmp/.X11-unix/X0: No such file or directory
Error: Can't open display: localhost:10.0

11.4 Tumbleweed 32 bit, 2 of them:
:~> xclock
Error: Can't open display:

All machines have it though:

$ ls /tmp/.X11-unix/X0

$ file /tmp/.X11-unix/X0
/tmp/.X11-unix/X0: socket

_Except_ 11.2 which I _can_ connect to, doen't have it:

$ ls /tmp/.X11-unix/X0
ls: cannot access /tmp/.X11-unix/X0: No such file or directory

So something has changed obviously.
What needs to be changed accordingly?
This socket lives in /tmp so maybe someone creates it by itself but how?

So far everything is like default I haven't changed anythig..

openSUSE 11.2 (x86_64) "Evergreen" main host
openSUSE 12.1 Milestone 5 (x86_64) 3.1.0-rc6-2-desktop in VBox
openSUSE 11.4 (i586) 3.0.4-43-desktop "Tumbleweed" in EeePC 900

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