Weirdness in RELENG_5 on amd64

Hi,

my dual Opteron server is experiencing strange problems; the same I've
been seeing since I installed it back in May. After a bit of uptime
(varies between 1-2 days and a month or two, depending on the kernel
release I am running) it will start acting up (if I'm lucky) or simply
panic. I have no panic message dump, since the box is very far away and
last time it paniced I had no serial console.

However yesterday it started acting up again: I was no longer able to
log in via SSH. Whenever I tried, the SSH client bailed out with the
message:
	ssh_exchange_identification: Connection closed by remote host
On my serial console I have syslog set to spew *.* on the console, but
there was absolutely no messages from sshd or any other source
whatsoever.

Running /etc/rc.d/sshd restart solved the problem - for now - but I'm
worried that this might be indicative of a more serious problem. I will
not be surprised if the box panics sometime in the next few hours or
days.

Anyone got any idea? This is a 12 day old build.

A related question: How do I make absolutely sure that kernel messages
are output on the serial console? I'm currently not sure this is the
case, so I don't know if I can even do anything when it crashes next
time. I've scanned through the handbook etc, but couldn't find any info.
Might have missed it, anyone care to enlighten me?

Thanks,
/Eirik