OK guys, I’ve resolved my issue with the EX4100. You won’t like the solution but its probably the only one…
I opened a support ticket with WD, described the problem, told them I had been fighting with this since April and I would like to return the hardware for any other WD product of approximate value ( could be hard drives I don’t care ). Just don’t send me back an EX4100 because I’m convinced there is a hardware or firmware problem and its not environmental.
So I did some basic diagnostics and sent them my logs, and at the end of the day they approved an RMA. I returned the EX4100 housing and they replaced it with a PR4100. I reinserted my drives, configured it like before, and the thing has been running for 15 days without a glitch.
So there it is. If your device is under warranty, return it. That’s what they carry insurance for.
EDIT - If you go this route, I have read that you should replace your drives in the same slots you removed them from. *