troubleshoot system freeze

I have an old Ultra 5 running NetBSD 6.1.5/sparc64 and it will randomly
freeze after long periods of time, 30 days or longer for example.  most
recently, the system was just idling as far as i know.  i brought up the
serial console that i connect to via minicom on Linux, and it
unfortunately did not display anything after the freeze... i was hoping
to at least have access to an ok> prompt or similar when the freeze
happened, therefore i was forced to physically hard reset the device in
order to get it going again.  i don't see any gz files in /var/crash to
analyze, just 'bounds' and 'minfree'.  the system is in a data center
with reliable power so i don't think it is a problem caused by a spike
electricity for example, but maybe the power did cause this??  in the
most recent episode, the last thing in the system log (messages) is a
standard message about syslogd restarting, but the freeze happened more
than 8 hours later when i noticed my ssh session dropped.

on another note does anyone know why syslogd restarts at weird intervals?

Oct  1 02:00:00   syslogd[154]: restart
Oct  1 11:00:01   syslogd[154]: restart
Oct  1 15:00:00   syslogd[154]: restart
Oct  1 20:00:00   syslogd[154]: restart
Oct  2 05:00:00   syslogd[154]: restart
Oct  2 14:00:00   syslogd[154]: restart
Oct  2 15:00:00   syslogd[154]: restart
Oct  2 23:00:00   syslogd[154]: restart
Oct  3 07:00:00   syslogd[154]: restart
Oct  3 15:00:00   syslogd[154]: restart
Oct  3 16:00:00   syslogd[154]: restart
Oct  4 01:00:00   syslogd[154]: restart
Oct  4 10:00:01   syslogd[154]: restart
Oct  4 15:00:01   syslogd[154]: restart
Oct  4 19:00:00   syslogd[154]: restart
<ssh session drops around Oct 5 03:17>
<physically reset system on Oct 16>:
Oct 16 14:00:09   syslogd[154]: restart
Oct 16 14:00:09   /netbsd: Copyright (c) 1996, 1997, 1998, 1999, 2000,
2001, 2002, 2003, 2004, 2005,
...