I have upgraded ±20 MP's the in last 6 months, its not that I'm doing this for the first time, you know.
I always run iStat before upgrading, to know what temperatures where there before the procedure! Very important!!
The spread between CPU A and B being 'always' 10-14c with ALL 0cto's I upgraded, made me aware about the NB.
Nobody really wants to tackle the NB if not really neccesary (broken rivet),...neither do/did I!!
When the temperature is staying below 80c why bother??
So finally a few weeks ago, when I took of the heatsink of CPU A, I saw a rivet snap...so I had no choice and had to fix it. Also this MP had a 12c spread between CPU A and B. After the fix the spread was only 5c.
I use Gelid GC Extreme, which looks identic to the paste that Apple uses.
When I remove a recently placed CPU, I have to twist the CPU to let go from the heatsink,...I explain this in detail to tell you I know what I'm doing!
So I can tell you 100% sure it is NOT an issue applying the paste!!
No accidental fix!!
The temperatures after the NB fix stay the same, just the Mac does not crash anymore!
The second 12-core I built for them, a week later, crashed in exactly the same way.
We swapped trays to see if it is a hardware issue,...nope...same problem.
The screenshot was taken ±2 minutes before the crash,...all is the same...but the CPU A can reach 76c now, without the Mac crashing.
I know this is NEW for everybody....the NB fix is also not hard to do, there has been written enough about that. I used the Chinese rivets.
PS, you are wrong stating that the CPU can reach 80c,...78c is shut-off for the X56...