In my case, I don't believe that any of the reported hardware is actually at fault. Here are my reasons: -
1. The R415/R515 pairs were bought 3 months apart. All four exhibit the same problems.
2. The errors have changed over time. I've had OEM errors, ECC errors, PSU errors, and CPU machine check errors.
3. There's a temporal element to the occurrences - roughly two days, two weeks, or six weeks.
4. The 'last error' IPMI command (I forget the specific command) shows a date of January 1970 (suggesting all zeros, and an invalid entry).
5. The machines otherwise run perfectly.
I'd put money on this being BMC related. There is a bug in these machines, which share a suspiciously similar chipset. Something's not playing ball.