You say UNIX but I'm wondering if you mean Linux?
What do you get from "uname -a" output?
Are you saying the "date" command gives you the correct time because it is synced to GPS? Is this done with ntp?
Does the hwclock command exist? It can be used to put the system time on the hardware clock. Most Linux systems have an init (boot script) that does this automatically during shutdown then they set the system time based on hardware clock during the boot.
Some systems have BIOS settings that tell the clock what to use so you might want to interrupt the boot and go into BIOS to see what, if any settings it offers.
Also the fact that the clock is reverting each time suggests your CMOS battery is defunct. Opening the system and locating this you may be able to find a replacement. (Many of these look like big watch batteries.)
As far as documentation goes. Web searches often help. I found several hits for your system board including this hardware manual: