Its got me stumped. Maybe the 212 has become warped on its base over time
or something
.
Surely you'd be able to see that from the TIM pattern that was left though?

Could be or the thremal paste is not the best.
Do a whole video edit and show what temps you get.
Ermmm...
Yes it's only a 212+, not a 212 Evo, but it shouldn't make that much difference should it? The 212 coolers are better than the stock coolers...normally...
The cooler base shouldn't have warped and yes, you'd see if there was a bad contact from the thermal paste residue.
It's still running warm, but that's not what I expected to see when you replaced with the stock cooler.
As I said earlier, I'm using a 212+ on a FX-8350 running at 4.5GHz on 1.428v (not a good chip).
I've not run IBT or Prime95, but doing a 1080p video encode in Handbrake (all 8 cores at around 99% usage) keeps my temps around 60-ish.

There on Auto and even after you change them they just go back to Auto
.