You could try some clean install again from tested sources one last time. You can't trust the original data.

Thanks jefro, but no. Setting up AC/DC with Samb4 is an arduous task related more to adding users, configuring workstations and setting up DNS and mail services than to installing the actual software. Both the test software used to stress and the actual server software were the same up-to-date versions of Slackware64 14.2. It took the real system almost 2 days to fail and I only ran the test system for 24 hours, so maybe it would have failed too in time.

The computer has been returned and I'm back to the rig that's been running for a couple of years without problem. It will likely be some time before Management approves such a venture again, but next time I'll try a different brand motherboard.